On Dec 23, 2012, at 12:37 AM, John Wilson wrote: From: <Paul_Koning at Dell.com> FWIW, DMC and DMR are the same at the programmer level. (Except for some trivial differences.) My notes say the limit on outstanding TX or RX buffers is 7 for DMC vs. 64 for DMR. Also, BSEL3 is a read/write reg that survives master clears on DMC but gives diag completion status on DMR (which is how INIT.SYS tells them apart). And opcode 02 is HALTR on DMR and reserved on DMC. Is there other stuff? I didn't know of those details, or other differences that matter to a driver. The way I've seen it done is that a DMC driver (7 buffers max) works fine for DMR, and there wasn't any real reason to do DMR-specific things. They are somewhat different at the protocol level -- DMC uses an older version of DDCMP and has some bugs in that implementation, especially in the "high speed" (1 Mb/s) version. Buggy WRT dealing with correct implementations, or buggy even talking to each other? Just curious (I have a pair of them around here somewhere). Buggy in the sense of not being 100% compliant to the DDCMP spec as written. They talk fine to each other. If you want to have another DDCMP implementation talk to them, you have to be aware of those details. I don't remember them but can find them if needed -- they would be in the NODVR (software DDCMP) RSTS/E driver sources. paul