Tarbell Electronics -- 1011A Floppy Disk Controller
Tarbell Electronics followed their popular Cassette
Interface with this FDC.
The Tarbell Floppy Disk Interface was a programmed-data-transfer (not DMA)
device utilizing Port I/O, similar for example to the
SD Systems Versafloppy boards. It was designed to work with a variety of
standard-size floppy disk drives. It includes a 32-byte ROM bootstrap program,
which was automatically enabled when the computer RESET button was pushed, and
which switched itself out after the bootstrap had run. In this way, no part of
the computer 64K of memory needed to be dedicated to Read-Only-Memory (ROM).
The interface ran at the standard speed of 250,000 bits per second, and the
normal formatted capacity per diskette of 256 kilobytes. Places for two
connectors were provided on the board. One 50-pin header connector and a cable
with the mating connector were provided with the interface kit. The drive end of
the cable has no connector, but a 50-pin edge connector could be added for an
There were four extra IC slots to allow you to do your own thing, and the
connector pins come out to jumper pads, so you can adapt to different drives.
The manual had the connections detailed for popular drives.
An on-board dip-switch was used to select the device address, disable the
bootstrap, and write-protect things. Circuitry was included to run up to four
drives, and eight could be accessed by using the spare IC slots. The Tarbell
Floppy Disk Interface and other related items could be bought in pieces,
so that was not necessary to make a single large outlay of cash.
The board utilized the Western Digital 1771-01 chip.
Tarbell also offering the (then new) CP/M floppy disk operating system
separately that was setup to work with the drive.
The very detailed and well written manual for this board can be obtained
Other Tarbell Electronics
Interface Single Density FDC
Double Density FDC
Z80 CPU Board
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