Double Density Controllers and TRS 80 Model I Expansion Unit

[billdeg]

This weekend I did some testing to compare the little-known Aeoromp Double Density Controller vs. the Tandy DDC. I did not test a Percom DDC, there is already plenty on the web about that one.

Test Units:
1) Three Expansion Interfaces (E/I's), one is a 26-1140 and two are 26-1142-1's.
26-1142-1 s/n 014121
26-1142-1 s/n 005581
26-1140 s/n 047396
they all work at least to the point to attempting to access the diskdrive for the OS.

2) Two Percom DD disk drives - wired together as drive 0 and 1. These were the test drives, but also tried Micropolis 1033 II dual floppy and a regular old Tandy mini floppy drive.

3) TRS 80 Model I with Level II Basic 26-1003, s/n 008498 works, extensively tested, my "test unit" for all testing.

TEST RESULTS

1) 26-1142-1 s/n 014121 with Aerocomp DDC and Percom DD disk drives

I was able to load DoubleDOS 4.23 and DOSPlus double density ver 3.4 48K using Percom drives. This is by far the best combination of drives, E/I and DDC.

2) 26-1142-1 s/n 014121 with Aerocomp DDC and Micropolis 1033 drive

I was not able to load DoubleDOS, only DOSPlus.

3) 26-1142-1 s/n 005581 with Tandy Factory-installed 26-1143 (Tandy) DDC and Percom Drives

I was *not* able to load DoubleDOS 4.23 nor "DOSPlus double density ver 3.4 48K" using Percom drives. I was able to load TRS DOS 2.3, which I don't believe to be a DD OS.

4) 26-1140 s/n 047396 with Misosys-installed 26-1143 (Tandy) DDC.

I was *not* able to load DoubleDOS 4.23 nor "DOSPlus double density ver 3.4 48K" using Percom drives. I was able to load TRS DOS 2.3, which I don't believe to be a DD OS.

5) 26-1140 s/n 047396 with Aerocomp DDC (swapped out the DDC's)

I was *not* able to load DoubleDOS 4.23 nor "DOSPlus double density ver 3.4 48K" using Percom drives. I was able to load TRS DOS 2.3.

CONCLUSION

The Aerocomp DDC seems to be most like the Percom DDC, not the Tandy DDC. In fact, I would guess that they are interchangeable.

The Tandy DDC does not work with any of the double-density type DOS's that I own, but I was focusing on the Aerocomp DDC, and I did not try every DOS I could have. I don't own every DOS for the Tandy TRS 80 Model I either. Who does?

The Aerocomp DDC may not be compatible with the Expansion Interface model 26-1140. I was unable to get the Aerocomp DDC to work in a 26-1140.

ALSO
All of the system combinations, when hooked to a standard Radio Shack 5 1/4" mini floppy drive could access a TRS DOS 2.3 SD disk.


The Micropolis 1033-II drive is semi-compatible with the Aerocomp DDC.

I would like someone else to try these same tests to see if they get the same results. These are old machines and I don't really like to keep pulling these controllers and chips in and out of the Expansion Interfaces. They did not always fit snuggly, and it's possible that if your DDC does not work you need to be extra sure that your chips are all of the way into the socket, and that the chips are not positioned upside-down.

I have Aerocomp DDC controllers for sale or trade if anyone wants one.

Bill Degnan
Wilmington, DE USA

[larryfos]

The Tandy DDC is not compatible with the Percom DDC. The DOS has to be patched to work with the Tandy DDC, after which it will not work with the Percom. I have both, and need to maintain two sets of DOS disks so I can use them both. No DOS that I know of will automatically recognize the doubler type and make the adjustments.

DOSPlus uses a patch file called RS.TXT to patch itself. LDOS uses a switch with LDUBL. TRSDOS 2.3 is SD, but 2.7DD is DD. NewDOS/80 needs to be zapped to work with the Tandy DDC.

[billdeg]

thanks