Parallel Bus Interface (PBI)

The Parallel Bus Interface or PBI is a 50-pin port found on some Atari 8-bit XL computers. It provides unbuffered, direct connection to the system bus lines (address, data, control), running at the same speed as the 6502 CPU.

Only the 600XL and 800XL computers had a PBI. XE systems came with the Enhanced Cartridge Interface (ECI), a functionally similar connection.

Details

During coldstart, the Atari OS polls for various parallel bus devices. If character devices are found, it'll load handler (aka driver) information into its handler table and initializes the parallel bus device, if needed.

Instead of loading a driver to RAM, a character device can utilize the Generic Parallel Device Handler that's already provided (at a fixed address in ROM) once the address is loaded into the handler table. The device connected to the parallel bus gets its ROM space mapped to the OS Floating-point package subroutines and tables. While the device is selected, no floating-point operations can take place. Once de-selected, the floating-point routines are restored.

A block device does not use the handler table, the only thing needed for proper initialization is setting a predefined flag, that the device is present. A block device can not use a softloaded driver, its driver must reside in the aforementioned ROM space.

Up to eight devices can be connected at a time. When they have been initialized properly, the OS selects them and deselects automatically as appropriate.

Pinout

Devices

*Atari 1064 Memory Module - Designed specifically for the 600XL, it upgraded the memory of the 600XL to 64kB. Only parallel bus device released by Atari.

*Atari 1090 Expansion System - Designed to give expansion slots to the XL computers. Never released.

*ICD Multi I/O Board - Hooked up to either a PBI or ECI connection. Featured a RAMdisk, parallel port, serial port, print spooler and a hard disk interface.

*Black Box - The Black Box by CSS hooks up to either PBI or ECI connection. Featured a SCSI interface, a serial port, parallel port, floppy drive interface and a built-in menu system.

*SupraDrive - an early SCSI disk drive.

ee also

*Enhanced Cartridge Interface (ECI)

References

* Chadwick, Ian (1985). "Mapping the Atari Revised Edition". COMPUTE! Publications, Inc. ISBN 0-87455-004-1. [http://www.atariarchives.org/mapping/]

External links

* [http://www.atarimagazines.com/v5n12/ICD.html ICD Boosts 8-bit Atari Power] Antic Magazine. Review on ICD products for the Atari.