Western Digital FD1771

Derivatives

• The FD1781 was designed for double density, but required external modulation and demodulation circuitry, so it could support MFM, M2FM, GCR or other double-density encodings.
• The FD1791-FD1797 series added internal support for double density modulation, compatible with the IBM System/34 disk format. They required an external data separator.
• The WD1761-WD1767 series were versions of the FD179x 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 8-in floppy drives or the later "high-density" or 90 mm floppy drives.
• The WD2791-WD2797 series 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 and drives.
• The WD1770, WD1772, and WD1773 added an internal digital data separator and write precompensator, eliminating the need for external passive components but raising 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 was a version of the chip that Atari fitted to the Atari STE which supported high density operation. After production at WD could not be sustained, Atari decided to license the design and modify it to get high density and extra density operation. The chip was codenamed "Ajax", had the number C302096 and was produced by Toshiba.

  Compatible chips

• FD179x series from SMC Microelectronics
• MB887x series from Fujitsu
• VL177x series from VLSI Technology.
• Soviet KR1818WG93 was a WD1793 analog