Cromemco 64FDC Instruction Manual
INTRODUCTION
The 64FDC, Cromemco's third-generation floppy disk
controller board, offers substantial feature and benefit
improvements. The 64FDC provides 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
handles up to 4 drives in a daisy-chain configuration,
although 16 drives may be chained if the drives decode
the 4 drive-select lines.
The 64FDC has fewer parts than its predecessor, the
16FDC
,
and is therefore more
reliable. Yet it has more
features.
The 64FDC supports the new slimline eight-inch drives
such as those featured in the Cromemco System 3A. it
also includes write precompensation to ensure that it
works reliably on the inner tracks of a wide variety of
eight-inch drives.
All timing on the 64FDC is referenced to an onboard
crystal clock. This includes the head-stepping rate,
the motor-turnoff -timer, interval timers, the watchdog
timer in the auto wait circuit, and the precompensation
delay in the write circuit.
The 64FDC includes an 8-channel interrupt system
connected to the flag bits of the disk controller. One
of the interrupt inputs can be connected to the crystal
clock for use with the real-time multiuser, multitasking
Cromix Operating System.
Single-density data is recorded in the FM format while
double-density data uses the MFM format. Density on a
given diskette may vary from track to track. Such
dual-density diskettes often require the first track to
contain a disk type specifier, written in single
density, which informs the operating system of the
density and number of sides of the remainder of the
diskette.
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