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
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
JFD-CP Parallel Port
PIN FUNCTION SOURCE
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
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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