WD1770
Encyclopedia
The FD1771 is the first in a line of floppy disk controller
s 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
.
These families were used in many microcomputer
s and home computer
s 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
.
Floppy disk controller
A floppy disk controller is a special-purpose chip and associated disk controller circuitry that directs and controls reading from and writing to a computer's floppy disk drive . This article contains concepts common to FDCs based on the NEC µPD765 and Intel 8072A or 82072A and their descendants,...
s produced by Western Digital
Western Digital
Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...
. It uses single density
Single density
Single density, often shortened SD, is a capacity designation on magnetic storage, usually floppy disks. It describes the use of an encoding of information using Frequency modulation, also known as biphase mark code....
(FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
) modulation and supports the IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
3740 disk format. It is packaged in a 40-pin DIP
Dual in-line package
In microelectronics, a dual in-line package is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board or inserted in a socket.A DIP is usually referred to as a DIPn, where n is...
.
Derivatives
The FD1771 was succeeded by many derivatives that were mostly software-compatible:- The FD1781 was designed for double densityDouble densityDouble density, often shortened DD, is a capacity designation on magnetic storage, usually floppy disks. It describes the use of an encoding of information, which can encode on average twice as many bits per time unit compared to single density...
, but required external modulation and demodulation circuitry, so it could support MFMModified Frequency ModulationModified Frequency Modulation, commonly MFM, is a line coding scheme used to encode the actual data-bits on most floppy disk formats, hardware examples include Amiga, most CP/M machines as well as IBM PC compatibles. Early hard disk drives also used this coding.MFM is a modification to the original...
, M2FM, or other double-density encodings. - The FD1791-FD1797 series added internal support for double densityDouble densityDouble density, often shortened DD, is a capacity designation on magnetic storage, usually floppy disks. It describes the use of an encoding of information, which can encode on average twice as many bits per time unit compared to single density...
(MFMModified Frequency ModulationModified Frequency Modulation, commonly MFM, is a line coding scheme used to encode the actual data-bits on most floppy disk formats, hardware examples include Amiga, most CP/M machines as well as IBM PC compatibles. Early hard disk drives also used this coding.MFM is a modification to the original...
) 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 (200 mm) floppy drives or the later "high-density" 5.25 inches (133 mm) or 90 mm floppy drives.
- The WD2791-WD2797 series added an internal data separator using an analog phase-locked loopPhase-locked loopA phase-locked loop or phase lock loop is a control system that generates an output signal whose phase is related to the phase of an input "reference" signal. It is an electronic circuit consisting of a variable frequency oscillator and a phase detector...
, with some external passive components required for the VCOVoltage-controlled oscillatorA voltage-controlled oscillator or VCO is an electronic oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the applied DC voltage, while modulating signals may also be fed into the VCO to cause frequency modulation or phase...
. They took a 1 MHz or 2 MHz clock and were intended for 8 inches (203 mm) and 5.25 inches (133 mm) 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, or 'Ajax', was a derivative chip fitted to the Atari STE which supported high density (500 kbit/s) operation.
Compatible chips
Many compatible chips were available from other vendors:- FD179x series from SMC Microelectronics
- MB887x series from FujitsuFujitsuis a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
- VL177x series from VLSI TechnologyVLSI TechnologyVLSI Technology, Inc was a company which designed and manufactured custom and semi-custom ICs. The company was based in Silicon Valley, with headquarters at 1109 McKay Drive in San Jose, California...
. - Soviet КР1818ВГ93 was a WD1793 clone
These families were used in many microcomputer
Microcomputer
A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers...
s and home computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
s including the Radio Shack TRS-80
TRS-80
TRS-80 was Tandy Corporation's desktop microcomputer model line, sold through Tandy's Radio Shack stores in the late 1970s and early 1980s. The first units, ordered unseen, were delivered in November 1977, and rolled out to the stores the third week of December. The line won popularity with...
, Acorn Electron
Acorn Electron
The Acorn Electron is a budget version of the BBC Micro educational/home computer made by Acorn Computers Ltd. It has 32 kilobytes of RAM, and its ROM includes BBC BASIC along with its operating system....
, BBC Master
BBC Master
The BBC Master was a home computer released by Acorn Computers in early 1986. It was designed and built for the British Broadcasting Corporation and was the successor to the BBC Micro Model B. The Master 128 remained in production until 1993....
, Atari ST
Atari ST
The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals...
, Acorn Archimedes
Acorn Archimedes
The Acorn Archimedes was Acorn Computers Ltd's first general purpose home computer to be based on their own ARM architecture.Using a RISC design with a 32-bit CPU, at its launch in June 1987, the Archimedes was stated as running at 4 MIPS, with a claim of 18 MIPS during tests.The name is commonly...
and the SAM Coupé
SAM Coupé
The SAM Coupé is an 8-bit British home computer that was first released in late 1989. It is commonly considered a clone of the Sinclair ZX Spectrum computer, since it features a compatible screen mode and emulated compatibility, and it was marketed as a logical upgrade from the Spectrum...
, as well as the +D
+D
The +D was a floppy disk and printer interface for the Sinclair ZX Spectrum home computer, developed as a successor to Miles Gordon Technology's earlier product, the DISCiPLE...
and DISCiPLE
DISCiPLE
The DISCiPLE was a floppy disk interface for the Sinclair ZX Spectrum home computer. Designed by Miles Gordon Technology, it was marketed by Rockfort Products and launched in 1986....
disk interfaces for the Sinclair ZX Spectrum and the Commodore 1581
Commodore 1581
The Commodore 1581 is a 3½ inch double sided double density floppy disk drive made by Commodore Business Machines primarily for its C64 and C128 home/personal computers. The drive stores 800 kilobytes using an MFM encoding but format different from both MS-DOS , and the Amiga formats. With...
for the Commodore 64
Commodore 64
The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...
.