WD1771

The WD1771 is the first in a line of floppy disk controllers produced by Western Digital. It uses single density (FM) modulation and supports the IBM 3740 disk format. It is packaged in a 40-pin DIP.

The WD1771 was succeeded by many derivatives that were mostly software-compatible:
*The WD1781 was designed for double density, but required external modulation and demodulation circuitry, so it could support MFM, M2FM, or other double-density encodings.
*The WD1791-WD1797 series added internal support for double density (MFM) modulation, compatible with the IBM System/34 disk format. They required an external data separator.
*The WD1761-WD1767 series were versions of the WD179x series rated for a maximum clock frequency of 1 MHz, resulting in a data rate limit of 125 kbit/s for single density and 250 kbit/s for double density, thus preventing them from being used for convert|8|in|mm|0|sing=on floppy drives or the later "high-density" convert|5.25|in|mm|0|sing=on or convert|90|mm|in|sing=on floppy drives.
*The WD2791-WD2797 series ( [http://tcg.speccy.cz/zoom/files/wd2797.pdf datasheet] ) added an internal data separator using an analog phase-locked loop, with some external passive components required for the VCO. They took a 1 MHz or 2 MHz clock and were intended for convert|8|in|mm|0|sing=on and convert|5.25|in|mm|0|sing=on drives.
*The WD1770, WD1772, and WD1773 ( [http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/wd177x/index.html datasheet images] ) added an internal digital data separator and write precompensator, eliminating the need for external passive components but upping the clock rate requirement to 8 MHz. They supported double density, despite the apparent regression of the part number, and were packaged in 28-pin DIP packages.
**The WD1772PH02-02, or 'Ajax', was a derivative chip fitted to the Atari STE which supported high density (500 kbit/s) operation.

Many compatible chips were available from other vendors:
*FD179x series from SMC Microelectronics
*MB887x series from Fujitsu
*VL177x series from VLSI Technology.

These families were used in many microcomputers and home computers including the Radio Shack TRS-80, Acorn Electron, BBC Master, Atari ST, Acorn Archimedes and the SAM Coupé, as well as the +D and DISCiPLE disk interfaces for the Sinclair ZX Spectrum and the Commodore 1581 for the Commodore 64.