PIC microcontroller

PIC microcontroller
PIC microcontrollers in DIP and QFN packages
16-bit 28-pin PDIP PIC24 microcontroller next to a metric ruler

PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1650[1][2] originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to "Peripheral Interface Controller".[3][4]

PICs are popular with both industrial developers and hobbyists alike due to their low cost, wide availability, large user base, extensive collection of application notes, availability of low cost or free development tools, and serial programming (and re-programming with flash memory) capability.

Microchip announced on February 2008 the shipment of its six billionth PIC processor.[5]

Contents

Core architecture

The PIC architecture is characterized by its multiple attributes:

  • Separate code and data spaces (Harvard architecture) for devices other than PIC32, which has a Von Neumann architecture.
  • A small number of fixed length instructions
  • Most instructions are single cycle execution (2 clock cycles, or 4 clock cycles in 8-bit models), with one delay cycle on branches and skips
  • One accumulator (W0), the use of which (as source operand) is implied (i.e. is not encoded in the opcode)
  • All RAM locations function as registers as both source and/or destination of math and other functions.[3]
  • A hardware stack for storing return addresses
  • A fairly small amount of addressable data space (typically 256 bytes), extended through banking
  • Data space mapped CPU, port, and peripheral registers
  • The program counter is also mapped into the data space and writable (this is used to implement indirect jumps).

There is no distinction between memory space and register space because the RAM serves the job of both memory and registers, and the RAM is usually just referred to as the register file or simply as the registers.

Data space (RAM)

PICs have a set of registers that function as general purpose RAM. Special purpose control registers for on-chip hardware resources are also mapped into the data space. The addressability of memory varies depending on device series, and all PIC devices have some banking mechanism to extend addressing to additional memory. Later series of devices feature move instructions which can cover the whole addressable space, independent of the selected bank. In earlier devices, any register move had to be achieved via the accumulator.

To implement indirect addressing, a "file select register" (FSR) and "indirect register" (INDF) are used. A register number is written to the FSR, after which reads from or writes to INDF will actually be to or from the register pointed to by FSR. Later devices extended this concept with post- and pre- increment/decrement for greater efficiency in accessing sequentially stored data. This also allows FSR to be treated almost like a stack pointer (SP).

External data memory is not directly addressable except in some high pin count PIC18 devices.

Code space

The code space is generally implemented as ROM, EPROM or flash ROM. In general, external code memory is not directly addressable due to the lack of an external memory interface. The exceptions are PIC17 and select high pin count PIC18 devices.[6]

Word size

All PICs handle (and address) data in 8-bit chunks. However, the unit of addressability of the code space is not generally the same as the data space. For example, PICs in the baseline and mid-range families have program memory addressable in the same wordsize as the instruction width, i.e. 12 or 14 bits respectively. In contrast, in the PIC18 series, the program memory is addressed in 8-bit increments (bytes), which differs from the instruction width of 16 bits.

In order to be clear, the program memory capacity is usually stated in number of (single word) instructions, rather than in bytes.

Stacks

PICs have a hardware call stack, which is used to save return addresses. The hardware stack is not software accessible on earlier devices, but this changed with the 18 series devices.

Hardware support for a general purpose parameter stack was lacking in early series, but this greatly improved in the 18 series, making the 18 series architecture more friendly to high level language compilers.

Instruction set

A PIC's instructions vary from about 35 instructions for the low-end PICs to over 80 instructions for the high-end PICs. The instruction set includes instructions to perform a variety of operations on registers directly, the accumulator and a literal constant or the accumulator and a register, as well as for conditional execution, and program branching.

Some operations, such as bit setting and testing, can be performed on any numbered register, but bi-operand arithmetic operations always involve W (the accumulator), writing the result back to either W or the other operand register. To load a constant, it is necessary to load it into W before it can be moved into another register. On the older cores, all register moves needed to pass through W, but this changed on the "high end" cores.

PIC cores have skip instructions which are used for conditional execution and branching. The skip instructions are 'skip if bit set' and 'skip if bit not set'. Because cores before PIC18 had only unconditional branch instructions, conditional jumps are implemented by a conditional skip (with the opposite condition) followed by an unconditional branch. Skips are also of utility for conditional execution of any immediate single following instruction.

The 18 series implemented shadow registers which save several important registers during an interrupt, providing hardware support for automatically saving processor state when servicing interrupts.

In general, PIC instructions fall into 5 classes:

  1. Operation on working register (WREG) with 8-bit immediate ("literal") operand. E.g. movlw (move literal to WREG), andlw (AND literal with WREG). One instruction peculiar to the PIC is retlw, load immediate into WREG and return, which is used with computed branches to produce lookup tables.
  2. Operation with WREG and indexed register. The result can be written to either the Working register (e.g. addwf reg,w). or the selected register (e.g. addwf reg,f).
  3. Bit operations. These take a register number and a bit number, and perform one of 4 actions: set or clear a bit, and test and skip on set/clear. The latter are used to perform conditional branches. The usual ALU status flags are available in a numbered register so operations such as "branch on carry clear" are possible.
  4. Control transfers. Other than the skip instructions previously mentioned, there are only two: goto and call.
  5. A few miscellaneous zero-operand instructions, such as return from subroutine, and sleep to enter low-power mode.

Performance

The architectural decisions are directed at the maximization of speed-to-cost ratio. The PIC architecture was among the first scalar CPU designs,[citation needed] and is still among the simplest and cheapest. The Harvard architecture—in which instructions and data come from separate sources—simplifies timing and microcircuit design greatly, and this benefits clock speed, price, and power consumption.

The PIC instruction set is suited to implementation of fast lookup tables in the program space. Such lookups take one instruction and two instruction cycles. Many functions can be modeled in this way. Optimization is facilitated by the relatively large program space of the PIC (e.g. 4096 x 14-bit words on the 16F690) and by the design of the instruction set, which allows for embedded constants. For example, a branch instruction's target may be indexed by W, and execute a "RETLW" which does as it is named - return with literal in W.

Interrupt latency is constant at three instruction cycles. External interrupts have to be synchronized with the four clock instruction cycle, otherwise there can be a one instruction cycle jitter. Internal interrupts are already synchronized. The constant interrupt latency allows PICs to achieve interrupt driven low jitter timing sequences. An example of this is a video sync pulse generator. This is no longer true in the newest PIC models, because they have a synchronous interrupt latency of three or four cycles.

Advantages

The PIC architectures have these advantages:

  • Small instruction set to learn
  • RISC architecture
  • Built in oscillator with selectable speeds
  • Easy entry level, in circuit programming plus in circuit debugging PICKit units available from Microchip.com for less than $50
  • Inexpensive microcontrollers
  • Wide range of interfaces including I²C, SPI, USB, USART, A/D, programmable comparators, PWM, LIN, CAN, PSP, and Ethernet[7]

Limitations

The PIC architectures have these limitations:

  • One accumulator
  • Register-bank switching is required to access the entire RAM of many devices
  • Operations and registers are not orthogonal; some instructions can address RAM and/or immediate constants, while others can only use the accumulator

The following stack limitations have been addressed in the PIC18 series, but still apply to earlier cores:

With paged program memory, there are two page sizes to worry about: one for CALL and GOTO and another for computed GOTO (typically used for table lookups). For example, on PIC16, CALL and GOTO have 11 bits of addressing, so the page size is 2048 instruction words. For computed GOTOs, where you add to PCL, the page size is 256 instruction words. In both cases, the upper address bits are provided by the PCLATH register. This register must be changed every time control transfers between pages. PCLATH must also be preserved by any interrupt handler.[8]

Compiler development

While several commercial compilers are available, in 2008, Microchip released their own C compilers, C18 and C30, for the line of 18F 24F and 30/33F processors.

The easy to learn RISC instruction set of the PIC assembly language code can make the overall flow difficult to comprehend. Judicious use of simple macros can increase the readability of PIC assembly language. For example, the original Parallax PIC assembler ("SPASM") has macros which hide W and make the PIC look like a two-address machine. It has macro instructions like "mov b, a" (move the data from address a to address b) and "add b, a" (add data from address a to data in address b). It also hides the skip instructions by providing three operand branch macro instructions such as "cjne a, b, dest" (compare a with b and jump to dest if they are not equal).

Family core architectural differences

Baseline core devices

These devices feature a 12-bit wide code memory, a 32-byte register file, and a tiny two level deep call stack. They are represented by the PIC10 series, as well as by some PIC12 and PIC16 devices. Baseline devices are available in 6-pin to 40-pin packages.

Generally the first 7 to 9 bytes of the register file are special-purpose registers, and the remaining bytes are general purpose RAM. Pointers are implemented using a register pair: after writing an address to the FSR (file select register), the INDF (indirect f) register becomes an alias for the addressed register. If banked RAM is implemented, the bank number is selected by the high 3 bits of the FSR. This affects register numbers 16–31; registers 0–15 are global and not affected by the bank select bits.

Because of the very limited register space (5 bits), 4 rarely-read registers were not assigned addresses, but written by special instructions (OPTION and TRIS).

The ROM address space is 512 words (12 bits each), which may be extended to 2048 words by banking. CALL and GOTO instructions specify the low 9 bits of the new code location; additional high-order bits are taken from the status register. Note that a CALL instruction only includes 8 bits of address, and may only specify addresses in the first half of each 512-word page.

Lookup tables are implemented using a computed GOTO (assignment to PCL register) into a table of RETLW instructions.

The instruction set is as follows. Register numbers are referred to as "f", while constants are referred to as "k". Bit numbers (0–7) are selected by "b". The "d" bit selects the destination: 0 indicates W, while 1 indicates that the result is written back to source register f. The C and Z status flags may be set based on the result; otherwise they are unmodified. Add and subtract (but not rotate) instructions that set C also set the DC (digit carry) flag, the carry from bit 3 to bit 4, which is useful for BCD arithmetic.

12-bit PIC instruction set
11 10 9 8 7 6 5 4 3 2 1 0 Mnemonic C? Z? Description
0 0 0 0 0 0 0 opcode Miscellaneous instructions
0 0 0 0 0 0 0 0 0 0 0 0 NOP No operation (MOVW 0,W)
0 0 0 0 0 0 0 0 0 0 1 0 OPTION Copy W to OPTION register
0 0 0 0 0 0 0 0 0 0 1 1 SLEEP Go into standby mode
0 0 0 0 0 0 0 0 0 1 0 0 CLRWDT Restart watchdog timer
0 0 0 0 0 0 0 0 0 1 f TRIS f Copy W to tri-state register (f = 1, 2 or 3)
0 0 opcode d register ALU operations: dest ← OP(f,W)
0 0 0 0 0 0 1 f MOVWF f dest ← W
0 0 0 0 0 1 d f CLR f,d Z dest ← 0, usually written CLRW or CLRF f
0 0 0 0 1 0 d f SUBWF f,d C Z dest ← f−W
0 0 0 0 1 1 d f DECF f,d Z dest ← f−1
0 0 0 1 0 0 d f IORWF f,d Z dest ← f|W, logical inclusive or
0 0 0 1 0 1 d f ANDWF f,d Z dest ← f&W, logical and
0 0 0 1 1 0 d f XORWF f,d Z dest ← f^W, logical exclusive or
0 0 0 1 1 1 d f ADDWF f,d C Z dest ← f+W
0 0 1 0 0 0 d f MOVF f,d Z dest ← f
0 0 1 0 0 1 d f COMF f,d Z dest ← ~f, bitwise complement
0 0 1 0 1 0 d f INCF f,d Z dest ← f+1
0 0 1 0 1 1 d f DECFSZ f,d dest ← f−1, then skip if zero
0 0 1 1 0 0 d f RRF f,d C dest ← CARRY*128 | f>>1, rotate right through carry
0 0 1 1 0 1 d f RLF f,d C dest ← F<<1 | CARRY, rotate left through carry
0 0 1 1 1 0 d f SWAPF f,d dest ← f<<4 | f>>4, swap nibbles
0 0 1 1 1 1 d f INCFSZ f,d dest ← f+1, then skip if zero
0 1 op bit register Bit operations
0 1 0 0 bit f BCF f,b Clear bit b of f
0 1 0 1 bit f BSF f,b Set bit b of f
0 1 1 0 bit f BTFSC f,b Skip if bit b of f is clear
0 1 1 1 bit f BTFSS f,b Skip if bit b of f is set
1 0 op k Control transfers
1 0 0 0 k RETLW k Set W ← k, then return from subroutine
1 0 0 1 k CALL k Call subroutine, 8-bit address k
1 0 1 k GOTO k Jump to 9-bit address k[9]
1 1 op 8-bit immediate Operations with W and 8-bit literal: W ← OP(k,W)
1 1 0 0 k MOVLW k W ← k
1 1 0 1 k IORLW k Z W ← k|W, bitwise logical or
1 1 1 0 k ANDLW k Z W ← k&W, bitwise and
1 1 1 1 k XORLW k Z W ← k^W, bitwise exclusive or
11 10 9 8 7 6 5 4 3 2 1 0 Mnemonic C? Z? Description

Mid-range core devices

These devices feature a 14-bit wide code memory, and an improved 8 level deep call stack. The instruction set differs very little from the baseline devices, but the increased opcode width allows 128 registers and 2048 words of code to be directly addressed. The mid-range core is available in the majority of devices labeled PIC12 and PIC16.

The first 32 bytes of the register space are allocated to special-purpose registers; the remaining 96 bytes are used for general-purpose RAM. If banked RAM is used, the high 16 registers (0x70–0x7F) are global, as are a few of the most important special-purpose registers, including the STATUS register which holds the RAM bank select bits. (The other global registers are FSR and INDF, the low 8 bits of the program counter PCL, the PC high preload register PCLATH, and the master interrupt control register INTCON.)

The PCLATH register supplies high-order instruction address bits when the 8 bits supplied by a write to the PCL register, or the 11 bits supplied by a GOTO or CALL instruction, is not sufficient to address the available ROM space.

14-bit PIC instruction set
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Mnemonic C? Z? Description
0 0 0 0 0 0 0 opcode Miscellaneous instructions
0 0 0 0 0 0 0 0 0 0 0 0 0 0 NOP No operation (MOVW 0,W)
0 0 0 0 0 0 0 0 0 0 1 0 0 0 RETURN Return from subroutine, W unmodified
0 0 0 0 0 0 0 0 0 0 1 0 0 1 RETFIE Return from interrupt
0 0 0 0 0 0 0 1 1 0 0 0 1 0 OPTION Copy W to OPTION register
0 0 0 0 0 0 0 1 1 0 0 0 1 1 SLEEP Go into standby mode
0 0 0 0 0 0 0 1 1 0 0 1 0 0 CLRWDT Restart watchdog timer
0 0 0 0 0 0 0 1 1 0 0 1 f TRIS f Copy W to tri-state register (f = 1, 2 or 3)
0 0 opcode d register ALU operations: dest ← OP(f,W)
0 0 0 0 0 0 1 f MOVWF f f ← W
0 0 0 0 0 1 d f CLR f,d Z dest ← 0, usually written CLRW or CLRF f
0 0 0 0 1 0 d f SUBWF f,d C Z dest ← f−W
0 0 0 0 1 1 d f DECF f,d Z dest ← f−1
0 0 0 1 0 0 d f IORWF f,d Z dest ← f|W, logical inclusive or
0 0 0 1 0 1 d f ANDWF f,d Z dest ← f&W, logical and
0 0 0 1 1 0 d f XORWF f,d Z dest ← f^W, logical exclusive or
0 0 0 1 1 1 d f ADDWF f,d C Z dest ← f+W
0 0 1 0 0 0 d f MOVF f,d Z dest ← f
0 0 1 0 0 1 d f COMF f,d Z dest ← ~f, bitwise complement
0 0 1 0 1 0 d f INCF f,d Z dest ← f+1
0 0 1 0 1 1 d f DECFSZ f,d dest ← f−1, then skip if zero
0 0 1 1 0 0 d f RRF f,d C dest ← CARRY*128 | f>>1, rotate right through carry
0 0 1 1 0 1 d f RLF f,d C dest ← f<<1 | CARRY, rotate left through carry
0 0 1 1 1 0 d f SWAPF f,d dest ← f<<4 | f>>4, swap nibbles
0 0 1 1 1 1 d f INCFSZ f,d dest ← f+1, then skip if zero
0 1 op bit register Bit operations
0 1 0 0 bit f BCF f,b Clear bit b of f
0 1 0 1 bit f BSF f,b Set bit b of f
0 1 1 0 bit f BTFSC f,b Skip if bit b of f is clear
0 1 1 1 bit f BTFSS f,b Skip if bit b of f is set
1 0 op k Control transfers
1 0 0 k CALL k Call subroutine
1 0 1 k GOTO k Jump to address k
1 1 op 8-bit immediate Operations with W and 8-bit literal: W ← OP(k,W)
1 1 0 0 x x k MOVLW k W ← k
1 1 0 1 x x k RETLW k W ← k, then return from subroutine
1 1 1 0 0 0 k IORLW k Z W ← k|W, bitwise logical or
1 1 1 0 0 1 k ANDLW k Z W ← k&W, bitwise and
1 1 1 0 1 0 k XORLW k Z W ← k^W, bitwise exclusive or
1 1 1 0 1 1 k (reserved)
1 1 1 1 0 x k SUBLW k C Z W ← k−W, subtract
1 1 1 1 1 x k ADDLW k C Z W ← k+W, add
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Mnemonic C? Z? Description

Enhanced Mid-range core devices

Enhanced Mid-range core devices introduce a deeper hardware stack, additional reset methods, 14 additional instructions and ‘C’ programming language optimizations. In particular. there are two INDF registers (INDF0 and INDF1), and two corresponding FSR register pairs (FSRnL and FSRnH). Special instructions use FSRn registers like address registers, with a variety of addressing modes.

14-bit enhanced PIC additional instructions
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Mnemonic C? Z? Description
0 0 0 0 0 0 0 opcode Miscellaneous instructions
0 0 0 0 0 0 0 0 0 0 0 0 0 1 RESET Software reset
0 0 0 0 0 0 0 0 0 0 1 0 1 0 CALLW Push PC, then jump to PCLATH:W
0 0 0 0 0 0 0 0 0 0 1 0 1 1 BRW PC ← PC + W, relative jump using W
0 0 0 0 0 0 0 0 0 1 0 n 0 0 MOVIW ++FSRn Z Increment FSRn, then W ← INDFn
0 0 0 0 0 0 0 0 0 1 0 n 0 1 MOVIW −−FSRn Z Decrement FSRn, then W ← INDFn
0 0 0 0 0 0 0 0 0 1 0 n 1 0 MOVIW FSRn++ Z W ← INDFn, then increment FSRn
0 0 0 0 0 0 0 0 0 1 0 n 1 1 MOVIW FSRn−− Z W ← INDFn, then decrement FSRn
0 0 0 0 0 0 0 0 0 1 1 n m MOVWI using FSRn INDFn ← W, same modes as MOVIW
0 0 0 0 0 0 0 0 1 k MOVLB k BSR ← k, move literal to bank select register
1 1 opcode d register ALU operations: dest ← OP(f,W)
1 1 0 1 0 1 d f LSLF f,d C Z dest ← f << 1, logical shift left
1 1 0 1 1 0 d f LSRF f,d C Z dest ← f >> 1, logical shift right
1 1 0 1 1 1 d f ASRF f,d C Z dest ← f >> 1, arithmetic shift right
1 1 1 0 1 1 d f SUBWFB f,d C Z dest ← f − W − 1 + C, subtract with carry
1 1 1 1 0 1 d f ADDWFC f,d C Z dest ← f + W + C, add with carry
1 1 opcode k Operations with literal k
1 1 0 0 0 1 0 n k ADDFSR FSRn,k FSRn ← FSRn + k, add 6-bit signed offset
1 1 0 0 0 1 1 k MOVLP k PCLATH ← k, move 7-bit literal to PC latch high
1 1 0 0 1 k BRA k PC ← PC + k, branch relative using 9-bit signed offset
1 1 1 1 1 1 0 n k MOVIW k[FSRn] Z W ← [FSRn+k], 6-bit signed offset
1 1 1 1 1 1 1 n k MOVWI k[FSRn] [FSRn+k] ← W, 6-bit signed offset
13 12 11 10 9 8 7 6 5 4 3 2 1 0 Mnemonic C? Z? Description

PIC17 high end core devices

The 17 series never became popular and has been superseded by the PIC18 architecture. It is not recommended for new designs, and availability may be limited.

Improvements over earlier cores are 16-bit wide opcodes (allowing many new instructions), and a 16 level deep call stack. PIC17 devices were produced in packages from 40 to 68 pins.

The 17 series introduced a number of important new features:

  • a memory mapped accumulator
  • read access to code memory (table reads)
  • direct register to register moves (prior cores needed to move registers through the accumulator)
  • an external program memory interface to expand the code space
  • an 8-bit x 8-bit hardware multiplier
  • a second indirect register pair
  • auto-increment/decrement addressing controlled by control bits in a status register (ALUSTA)

PIC18 high end core devices

Microchip introduced the PIC18 architecture in 2000. [4] Unlike the 17 series, it has proven to be very popular, with a large number of device variants presently in manufacture. In contrast to earlier devices, which were more often than not programmed in assembly, C has become the predominant development language [5].

The 18 series inherits most of the features and instructions of the 17 series, while adding a number of important new features:

  • much deeper call stack (31 levels deep)
  • the call stack may be read and written
  • conditional branch instructions
  • indexed addressing mode (PLUSW)
  • extending the FSR registers to 12 bits, allowing them to linearly address the entire data address space
  • the addition of another FSR register (bringing the number up to 3)

The auto increment/decrement feature was improved by removing the control bits and adding four new indirect registers per FSR. Depending on which indirect file register is being accessed it is possible to postdecrement, postincrement, or preincrement FSR; or form the effective address by adding W to FSR.

In more advanced PIC18 devices, an "extended mode" is available which makes the addressing even more favorable to compiled code:

  • a new offset addressing mode; some addresses which were relative to the access bank are now interpreted relative to the FSR2 register
  • the addition of several new instructions, notable for manipulating the FSR registers.

These changes were primarily aimed at improving the efficiency of a data stack implementation. If FSR2 is used either as the stack pointer or frame pointer, stack items may be easily indexed—allowing more efficient re-entrant code. Microchip's MPLAB C18 C compiler chooses to use FSR2 as a frame pointer.

PIC24 and dsPIC 16-bit microcontrollers

In 2001, Microchip introduced the dsPIC series of chips,[10] which entered mass production in late 2004. They are Microchip's first inherently 16-bit microcontrollers. PIC24 devices are designed as general purpose microcontrollers. dsPIC devices include digital signal processing capabilities in addition.

Architecturally, although they share the PIC moniker, they are very different from the 8-bit PICs. The most notable differences are:[11]

  • they feature a set of 16 working registers (W0-W15)
  • they fully support a stack in RAM, and do not have a hardware stack
  • bank switching is not required to access RAM or special function registers
  • data stored in program memory can be accessed directly using a feature called Program Space Visibility
  • interrupt sources may be assigned to distinct handlers using an interrupt vector table

Some features are:

  • hardware MAC (multiply–accumulate)
  • barrel shifting
  • bit reversal
  • (16×16)-bit single-cycle multiplication and other DSP operations
  • hardware divide assist (19 cycles for 16/32-bit divide)
  • hardware support for loop indexing
  • Direct memory access

dsPICs can be programmed in C using Microchip's C30 compiler which is a variant of gcc.

PIC32 32-bit microcontrollers

In November 2007 Microchip introduced the new PIC32MX family of 32-bit microcontrollers. The initial device line-up is based on the industry standard MIPS32 M4K Core[6]. The device can be programmed using the Microchip MPLAB C Compiler for PIC32 MCUs, a variant of the GCC compiler. The first 18 models currently in production (PIC32MX3xx and PIC32MX4xx) are pin to pin compatible and share the same peripherals set with the PIC24FxxGA0xx family of (16-bit) devices allowing the use of common libraries, software and hardware tools.

The PIC32 architecture brings a number of new features to Microchip portfolio, including:

  • The highest execution speed 80 MIPS (120+[12] Dhrystone MIPS @ 80 MHz)
  • The largest flash memory: 512 kByte
  • One instruction per clock cycle execution
  • The first cached processor
  • Allows execution from RAM
  • Full Speed Host/Dual Role and OTG USB capabilities
  • Full JTAG and 2 wire programming and debugging
  • Real-time trace

Device variants and hardware features

PIC devices generally feature:

  • Sleep mode (power savings).
  • Watchdog timer.
  • Various crystal or RC oscillator configurations, or an external clock.

Variants

Within a series, there are still many device variants depending on what hardware resources the chip features.

  • General purpose I/O pins.
  • Internal clock oscillators.
  • 8/16/32 Bit Timers.
  • Internal EEPROM Memory.
  • Synchronous/Asynchronous Serial Interface USART.
  • MSSP Peripheral for I²C and SPI Communications.
  • Capture/Compare and PWM modules.
  • Analog-to-digital converters (up to ~1.0 MHz).
  • USB, Ethernet, CAN interfacing support.
  • External memory interface.
  • Integrated analog RF front ends (PIC16F639, and rfPIC).
  • KEELOQ Rolling code encryption peripheral (encode/decode)
  • And many more.

Trends

The first generation of PICs with EPROM storage are almost completely replaced by chips with Flash memory. Likewise, the original 12-bit instruction set of the PIC1650 and its direct descendants has been superseded by 14-bit and 16-bit instruction sets. Microchip still sells OTP (one-time-programmable) and windowed (UV-erasable) versions of some of its EPROM based PICs for legacy support or volume orders. The Microchip website lists PICs that are not electrically erasable as OTP despite the fact that UV erasable windowed versions of these chips can be ordered..

History

The original PIC was built to be used with General Instruments' new 16-bit CPU, the CP1600. While generally a good CPU, the CP1600 had poor I/O performance, and the 8-bit PIC was developed in 1975 to improve performance of the overall system by offloading I/O tasks from the CPU. The PIC used simple microcode stored in ROM to perform its tasks, and although the term was not used at the time, it shares some common features with RISC designs.

In 1985, General Instruments spun off their microelectronics division and the new ownership cancelled almost everything — which by this time was mostly out-of-date. The PIC, however, was upgraded with internal EPROM to produce a programmable channel controller and today a huge variety of PICs are available with various on-board peripherals (serial communication modules, UARTs, motor control kernels, etc.) and program memory from 256 words to 64k words and more (a "word" is one assembly language instruction, varying from 12, 14 or 16 bits depending on the specific PIC micro family).

PIC and PICmicro are registered trademarks of Microchip Technology. It is generally thought that PIC stands for Peripheral Interface Controller, although General Instruments' original acronym for the initial PIC1640 and PIC1650 devices was "Programmable Interface Controller".[3] The acronym was quickly replaced with "Programmable Intelligent Computer".[4]

Various older (EPROM) PIC microcontrollers

The Microchip 16C84 (PIC16x84), introduced in 1993 , was the first[citation needed] Microchip CPU with on-chip EEPROM memory. This electrically erasable memory made it cost less than CPUs that required a quartz "erase window" for erasing EPROM.

PIC clones

Third party manufacturers make compatible products, for example the Parallax SX

Development tools

Microchip provides a freeware IDE package called MPLAB, which includes an assembler, linker, software simulator, and debugger. They also sell C compilers for the PIC18 and dsPIC which integrate cleanly with MPLAB. Free student versions of the C compilers are also available with all features. But for the free versions, optimizations will be disabled after 60 days.[13]

Several third parties make C language compilers for PICs, many of which integrate to MPLAB and/or feature their own IDE. A fully featured compiler for the PICBASIC language to program PIC microcontrollers is available from meLabs, Inc.

Development tools are available for the PIC family under the GPL or other free software or open sources licenses.

Device programmers

A development board for low pin-count MCU, from Microchip

Devices called "programmers" are traditionally used to get program code into the target PIC. Most PICs that Microchip currently sell feature ICSP (In Circuit Serial Programming) and/or LVP (Low Voltage Programming) capabilities, allowing the PIC to be programmed while it is sitting in the target circuit. ICSP programming is performed using two pins, clock and data, while a high voltage (12V) is present on the Vpp/MCLR pin. Low voltage programming dispenses with the high voltage, but reserves exclusive use of an I/O pin and can therefore be disabled to recover the pin for other uses (once disabled it can only be re-enabled using high voltage programming).

There are many programmers for PIC microcontrollers, ranging from the extremely simple designs which rely on ICSP to allow direct download of code from a host computer, to intelligent programmers that can verify the device at several supply voltages. Many of these complex programmers use a pre-programmed PIC themselves to send the programming commands to the PIC that is to be programmed. The intelligent type of programmer is needed to program earlier PIC models (mostly EPROM type) which do not support in-circuit programming.

Many of the higher end flash based PICs can also self-program (write to their own program memory). Demo boards are available with a small bootloader factory programmed that can be used to load user programs over an interface such as RS-232 or USB, thus obviating the need for a programmer device. Alternatively there is bootloader firmware available that the user can load onto the PIC using ICSP. The advantages of a bootloader over ICSP is the far superior programming speeds, immediate program execution following programming, and the ability to both debug and program using the same cable.

Microchip PICSTART Plus programmer

Programmers/debuggers are available directly from Microchip. Third party programmers range from plans to build your own, to self-assembly kits and fully tested ready-to-go units. Some are simple designs which require a PC to do the low-level programming signalling (these typically connect to the serial or parallel port and consist of a few simple components), while others have the programming logic built into them (these typically use a serial or USB connection, are usually faster, and are often built using PICs themselves for control).

Debugging

Software emulation

Commercial and free emulators exist for the PIC family processors.

In-circuit debugging

Later model PICs feature an ICD (in-circuit debugging) interface, built into the CPU core. ICD debuggers (MPLAB ICD2 and other third party) can communicate with this interface using three lines. This cheap and simple debugging system comes at a price however, namely limited breakpoint count (1 on older pics 3 on newer PICs), loss of some IO (with the exception of some surface mount 44-pin PICs which have dedicated lines for debugging) and loss of some features of the chip. For small PICs, where the loss of IO caused by this method would be unacceptable, special headers are made which are fitted with PICs that have extra pins specifically for debugging.

In-circuit emulators

Microchip offers three full in circuit emulators: the MPLAB ICE2000 (parallel interface, a USB converter is available); the newer MPLAB ICE4000 (USB 2.0 connection); and most recently, the REAL ICE. All of these ICE tools can be used with the MPLAB IDE for full source-level debugging of code running on the target.

The ICE2000 requires emulator modules, and the test hardware must provide a socket which can take either an emulator module, or a production device.

The REAL ICE connects directly to production devices which support in-circuit emulation through the PGC/PGD programming interface, or through a high speed connection which uses two more pins. According to Microchip, it supports "most" flash-based PIC, PIC24, and dsPIC processors.[14]

The ICE4000 is no longer directly advertised on Microchip's website, and the purchasing page states that it is not recommended for new designs.

PICKit 2 open source structure and clones

PICKit 2 has been an interesting PIC programmer from Microchip. It can program all PICs and debug most of the PICs (as of May-2009, only the PIC32 family is not supported for MPLAB debugging). Ever since its first releases, all software source code (firmware, PC application) and hardware schematic are open to the public. This makes it relatively easy for an end user to modify the programmer for use with a non-Windows operating system such as Linux or Mac OS. In the mean time, it also creates lots of DIY interest and clones. This open source structure brings many features to the PICKit 2 community such as Programmer-to-Go, the UART Tool and the Logic Tool, which have been contributed by PICKit 2 users. Users have also added such features to the PICKit 2 as 4MB Programmer-to-go capability, USB buck/boost circuits, RJ12 type connectors and others.

Part number suffixes

The F in a name generally indicates the PICmicro uses flash memory and can be erased electronically. A C generally means it can only be erased by exposing the die to ultraviolet light (which is only possible if a windowed package style is used). An exception to this rule is the PIC16C84 which uses EEPROM and is therefore electrically erasable.

An L in the name indicates the part will run at a lower voltage, often with frequency limits imposed.[15]

Parts designed specifically for low voltage operation, within a strict range of 3 - 3.6 Volts, are marked with a J in the part number. These parts are also uniquely I/O tolerant as they will accept up to 5V as inputs.[15]

See also

References

  1. ^ http://www.datasheetarchive.com/dl/Databooks-1/Book241-407.pdf
  2. ^ "PICmicro Family Tree", PIC16F Seminar Presentation http://www.microchip.com.tw/PDF/2004_spring/PIC16F%20seminar%20presentation.pdf
  3. ^ a b "MOS DATA 1976", General Instrument 1976 Databook
  4. ^ a b "1977 Data Catalog", Micro Electronics from General Instrument Corporation http://www.rhoent.com/pic16xx.pdf
  5. ^ "Microchip Technology Delivers Six Billionth PIC Microcontroller" (Press release). Microchip Technology. 27 February 2008. http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2018&mcparam=en534302. 
  6. ^ "AN869: External Memory Interfacing Techniques for the PIC18F8XXX". http://ww1.microchip.com/downloads/en/AppNotes/00869b.pdf. Retrieved 24 August 2009. 
  7. ^ Microchip Product Selector[1]
  8. ^ "PIC Paging and PCLATH"
  9. ^ PIC10F200/202/204/206 Data Sheet. Microchip Technology. 2007. p. 52. http://ww1.microchip.com/downloads/en/DeviceDoc/41239D.pdf. 
  10. ^ [2]
  11. ^ "PIC24H Family Overview". http://ww1.microchip.com/downloads/en/DeviceDoc/70166A.pdf. Retrieved 23 September 2007. 
  12. ^ "32-bit PIC® MCUs". http://www.microchip.com/en_US/family/pic32/. Retrieved 13 October 2010. 
  13. ^ "MPLAB C Compiler for PIC18 MCUs". http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en010014. 
  14. ^ "MPLAB REAL ICE In-Circuit Emulator Product Overview". http://ww1.microchip.com/downloads/en/DeviceDoc/51630a.pdf. Retrieved 23 September 2007. 
  15. ^ a b "3V Design Center". http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2530. Retrieved 2 August 2011. 

External links


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