J&M Disk Controllers for Color Computer

J&M Sytems produced Disk Controllers and complete drive systems including a hard drive system.  There were 3 different controllers, the original JFD-COCO, the JFD-CP and the later JFD-EC. The JFD-COCO was not compatible with a CoCo3, the JFD-EC was introduced  for the CoCo3. The JFD-CP features a parallel port to drive a Centronics compatible printer or the J&M hard drive.


This was the "classic" J&M controller. It had a 24 pin rom socket, that usually came with a  JDOS rom in it. This controller had gold contacts on both ends of the board. Utilized a Synertek SY6591 controller chip, also socketed. This was a good controller till the CoCo3 came out, and it did not work with it. J&M initially recommended changing the 74LS04 to a 7404, but this did not always solve the incompatibility. The final modification was to substitute the Q clock signal in place of the E clock, basically a trace cut and adding a jumper. Simply cut the E clock line (Pad 6). Solder a jumper wire to the Q clock (Pad 7) and connect it to the controller. I used a through hole beside U17 to make the connection on one controller I modified. The controller will now work with the CoCo3 and the CoCo2.  If you have a 24 pin JDOS rom, it will also not work with the CoCo3, swap in a RS DOS 1.1 or something such as ADOS 3. See Rainbow, May '87, page 174 for more information.


This was the second and most deluxe controller that J&M built for the CoCo. Externally it appears different than the original as there is now a toggle switch to select which rom to use, and a header connector which is the built in parallel port. The Hard Drive unit to connect to this controller was originally a 5 Mb Seagate, enclosed in a self contained drive/power unit with built in interface that connected directly to the Centronics compatible printer port. Software to drive it was OS-9 only.

JFD board layout

JFD-CP Parallel Port

1      Write Strobe       Controller
3      D0                      Bi-directional
5      D1                              "
7      D2                              "
9      D3                              "
11    D4                              "
13    D5                              "
15    D6                              "
17    D7                              "
19    Read Strobe       Controller
21    Busy                   External Device
23    N/C
25    Status                 External Device
26    Reset                  Controller

All even pins 2-24 are ground

This connector will allow most Centronics compatible printers to operate with the JFD-CP using a standard, unmodified Radio Shack Model 100 printer cable.

Pinout from page B-3, JDOS Disk Basic Reference Manual, J&M Systems


The EC stands for economy. This controller was brought out to get J&M back into the lower cost segment of the disk controller market. This controller  has a toggle switch to select one of the dual roms, and now supports a 16K device. Cost savings were obtained by eliminating the parallel port , and utilizing the  SY6591 controller chip, which J&M apparently bought the entire inventory of when Synertek went out of business.

Thanks to Alan Stallings, formerly of J&M, for correcting some errors and providing more information.

Page last updated Dec 24/2001

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