2024-03-02: The wiki ran out of disk space, so things were not working. This has been resolved by adding another 5GB of quota ;-) Thanks to Tim Lindner for reporting the issues. 2020-05-17: If a page gives you an error about some revision not being found, just EDIT the page and the old page should appear in the editor. If it does, just SAVE that and the page should be restored. OS-9 Al (talk) 12:22, 17 May 2020 (CDT)


From CoCopedia - The Tandy/Radio Shack Color Computer Wiki
Jump to navigation Jump to search
Looking for CoCo help? If you are trying to do something with your old Color Computer, read this quick reference. Want to contribute to this wiki? Be sure to read this first. This CoCo wiki project was started on October 29, 2004. --OS-9 Al

See Recent Changes. | About this site. | Join the E-Mail List or Facebook Group. | Contact me with updates/questions.

This page was last updated on 12/29/2014. Total Pages: 730. Total Files: 993.

Home / Hardware - J&M/Owl-Ware

J&M disk controller

J&M Systems, LTD. CoCo disk controller cart

Considered one of the best disk controllers for the TRS-80 Color Computers. They have gold connectors and are engineered to a very high standard

Internally has JDOS 1.11 rom on it for fast (6ms) disk drive stepping.

(8/7/12) I've just made a video of this great controller in action on my Coco 3: youtube J&M disk controller for Tandy TRS-80 Coco Color Computer

From: [1]

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-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