Tarbell S-100 boards and docs

This page last updated Dec 22 2013. Copyright Herb Johnson 2013.

Don Tarbell was an early developer of S-100 cards, beginning with the Tarbell Cassette Interface card in 1977. This card used a manual audio cassette tape recorder to store and recall programs. Cassette storage was popular in the years before floppy disk drives and controllers were available and affordable. Tarbell went on to produce a popular single-density floppy disk controller card among other S-100 cards and systems.

Here's some comments from Barry Watzman, a former Heath/Zenith engineer in the S-100 era, about Tarbell's floppy controller, as posted in comp.os.cpm from late 2009. Barry Watzman died in June 2010, see this linked Web page for a tribute. - Herb.

"The Tarbell single density board and the NorthStar [MDS floppy controller] board were key products in moving most 1970's hobbyists from cassette and paper tape to floppy diskette. They were probably the most important two floppy disk controller products of the era."

"There was ***NO*** standard layout for double density diskettes, either 8" or 5.25". It was a "do your own thing" world. Only SSSD 8" had a standard format."

"Versions of the Tarbell double density board prior to Revision E were horrid and unstable. Revision E and later generally worked ok, but the board was revised to at least a revsion "H" board. One problem with that board was that the power regulator was grossly over-stressed to the point that the fiberglass usually was burned and discolored around the voltage regulator. A common "jury rig" was to put a low value power resistor across the regulator on the back side of the board to "bleed off" some of it's load (under 10 ohms, 2 to 5 watts). [The tarbell DD board was not the only board to have such a problem]."- Barry Watzman

My colleague Josh Bendsaon has some observations about the WD1771 floppy controller chip in use. Here's Josh's 2013 notes about missing clocks, data separators, and the WD1771.

Tarbell docs

Tarbell Floppy disk Interface (M1011 8-inch single density), 1978, no revision. 92 pgs
Tarbell Floppy disk Interface (M1011 8-inch single density), 1979, rev C or D. 92 pgs
Tarbell Cassette Interface M1001, Jan 1977, w/ Kansas City s/w listing, 44 pgs
Tarbell Cassette Interface M1001, Mar 1977, w/ Kansas City s/w listing, 44 pgs
Tarbell Double Density COntroller, M2022, schematics & sources, 140 pgs
Tarbell Double Density Disk Interface manual, May 1980 rev E. 64 pgs plus 8 page schematic
---(excluding many pages of IC data sheets)
Duplex 816 Software Users Guide, Dec 1984, 16 p
Duplex 816 Hardware Manual Rev A May 1985. data sheets, schematics. 117 pgs
PCPROM notes for Duplex 816 system, Feb 85, 5 pgs
Concurrent CP/M 86 note for Duplex 816, 1 pg
Empire 16 Winchester setup notes, 1 pg
Tarbell CPU I/O board Model 3033 manual, 36 pgs + 42 pgs chip datasheets

Tarbell notes and addenda:
Double Density, 1979-81, 15 pgs
Tarbell flyers, 1979 price sheets, ads - ask for details
Tarbell BIOS assembled listing, March 1981, CP/M 2.2, double density - 18 pgs
Tarbell BIOS source listing, Nov 1980, CP/M 2.2, double density - 22 pgs
Tarbell cold loader source, 7/80, 4 pgs
Tarbell disk format, June 1979, single density, 9 pgs
Tarbell Double Density testing code, 6 pgs

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Herb Johnson
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