The FDC-II features include an on-board data buffer which allowed operation independent of the CPU. Thus. the FDC-II did not require any particular processor speed nor continuous processor overhead when transferring data to or from the floppy disk drive. Data transfer to the system was accomplished by memory-to-memory move instructions because the FDC-II occupied a space in the microprocessor memory field. DMA was not used, avoiding the compatibility problems which often arise from DMA operations.
FLOPPY DISK CONTROL
A NEC uPD765 LSI controller was used. This chip allowed single-and double-density data storage on both mini- and maxi-floppy drives providing the following capabilities which minimize overhead burden on the CPU and software:
Control up to four 8″ and four 5″ drives simultaneously under software control.
Single or double-density data transfer is under software control
Simultaneously perform seek operations on all drives connected to the system.
IBM diskette formatting provides for ease of information exchange with IBM-compatible controllers using similar operating system software.
Compatible with most double and single-sided drives (i.e., GSI, Siemens, Shugart. Micropolis, PerSci, Remex, Innotronics. MFE. Qume and any other ANSI-compatible flexible disk drive).
Automatically read sequential sectors on a diskette.
With appropriate software, the uPD765 could automatically read both tracks of a two-sided diskette.
Maximum formatted data storage available was 286k bytes for a double-sided mini-diskette and 1024k bytes on a double-sided maxi-diskette.
Under software control, record (sector) sizes of 128 (single density only). 256. 512, or 1024 bytes could be selected.
OPERATIONAL FEATURES
Phase Locked Oscillator (PLO) — An on-board phase-locked oscillator is used to stablize separated information and clock for precise data recovery.
1K RAM data buffer.
An on-board 2708 EPROM provided a bootstrap program for a disk operating system The 2708 could be easily altered by the user for his particular system. The FDC-II could also use the newer 2758 EPROMs.
Pre-write compensation wass used when writing to the disk drive for more precise data encoding.
Did not require processor overhead when data are transferring to or from the disk drive
Motor control was provided for mini-drives or PerSci drives.
Both the bootstrap EPROM and the data buffer activated the S-100 phantom line when accessed.
INTERFACE FEATURES
I/O and memory addressing were jumper selectable
ANSI-standard disk drive interface. A 50-pin and a 34-pm header are provided on the board.
A parallel port was provided for the user. This port provides 2 lines of input and 2 lines of output data
Any S-100 compatible CPU could be used with the FDC-II regardless of clock speed, but boot software in the on-board EPROM was compatible only with the 8080 and Z-80 families.
CPM and OASIS compatible.
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