S100 Computers - Cromemco 64 FDC

The 64FDC provided a complete system for floppy disk operation: serial I/O for an RS-232 terminal, a read only memory programmed with system bootstrap and diagnostic routines, and full read/write/format capability for any combination of single or double sided, single or double density, 5" (mini) or 8" (maxi) floppy disks. The 64FDC normally handled up to 4 drives in a daisy-chain configuration, although 16 drives may be chained if the drives decode the 4 drive-select lines completely. The 64FDC had fewer parts than its predecessor, the 16FDC, and was therefore more reliable. Yet it had more features. The 64FDC supported the then new slim line eight-inch drives such as those featured in the Cromemco System 3A. It also included write pre-compensation to ensure that it worked reliably on the inner tracks of a wide variety of eight-inch drives. All timing on the 64FDC was referenced to an onboard crystal clock. This included the head-stepping rate, the motor-turnoff timer, interval timers, the watchdog timer in the auto wait circuit, and the pre-compensation delay in the write circuit. The 64FDC included an 8-channel interrupt system connected to the flag bits of the disk controller. One of the interrupt inputs could be connected to the crystal clock for use with the real-time multiuser, multitasking Cromemco Cromix Operating System. Single-density data was recorded in the FM format while double-density data uses the MFM format. Like the Vector Graphics FDC, Cromemco utilized the 1793 chip rather than the 1791 (inverted data bus) chip. If you need to find out more about these chips see here.

The very extensive manual from Cromemco for this board can be obtained here.

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