In the manual the FDC-2 may be parsed
out into separate functional areas for easier understanding. These are:-
Disk Controller
This area of the FDC-2 interfaces directly with the disk drives. It can be instructed
by the CPU to select one of four drives, move the recording head in .a specified
drive to a specified track position, read a specified quantity of data from a drive,
write a quantity of data to a drive, format a disk, and even compare data on the
disk to system data. The controller also performs CRC checks on all disk data to
establish that data's validity.
DMA Controller
This functional area of the FDC-2 is dedicated to the direct transfer of data between
the Disk Controller and the user's system memory- The DMA controller has the ability
to disable the system CPU asynchronously to program execution, whenever the Disk
Controller indicates readiness for data transfer. Once the CPU is disabled the DMA
Controller will either read a byte from system memory and send it to the Disk controller,
or read a byte from the Disk Controller and write it into system memory. After the
DMA transfer, the CPU is re-enabled and will continue program, execution. The user
may program the DMA Controller to access any area of an IEEE 696.2 S-1QQ 16Mg address
space.
Addressing
The FDC-2 occupies 16 consecutive locations of system I/O space„ The. function assignment
of each of these locations is shown in the FDC-2 Address Map. The user may jumper
select the board location at any 16-location boundary in the standard IEEE S-100
64k I/O space. Optionally^ of course, the 8-bit I/O address space may be referenced
instead.
Onboard EPROM
Provision is made for a 2708 EPROM on the FDC-2 so that bootstrap firmware for the
user's operating system may be located on the board. The EPROM circuitry has its
own independent address. The user may jumper-select any 1K location in the extended
16 Mg system memory to locate the EPROM. The board may be configured so that PHANTOM
is driven when the EPROM is accessed, thus allowing the FDC-2 EPROM to overlay RAM
memory that responds to PHANTOM S-100 line, the EPROM — and the PHANTOM overlaying
signal — may be disabled with software. (The EPROM is enabled automatically when
power is applied and RESET* goes active.)
The manual for this
card can be downloaded
here.
