L.S. With a bit time on hand and the standstill after Paul's initial test from dup to pydecnet which appeared to be successful, I now undertook a test as Mark liked to have it preferably. So I did a fresh netgen on a simple configuration from simple basic install Rsx11MP system for only a Decnet end-node with one single Dup line communicating to a known working Pdp11 Rsx11MP Dmc circuit. I saw no difference from what I reported initially and later with logging, as was to be expected; my complex setup behaves exactly the same in this respect as it does for years in a complex network setup for Rsx and Rsts, and RT11 without network. This is on a Windows-2008R2 server and I suspect Paul did his test on unix/linux , however although it differs, that should be moot as far as Simh is concerned. There could be another difference though. Paul would probably have taken the default route and used Ddcmp withouth KG11 support: Dup without Kdp is the only sync line to use it, though async Decnet DL/DZ/VH might use it as well. As I prefer the most complex configs possible (any two of a kind where possible as Dec used to have them), I do also employ the KG11, so for Dup support it will be used when configured so in Decnet11MP. On a sim it is not that effective, but in hardware in the past it did make a difference for fast crc computing. So I retested with no KG11 support and indeed, now the Dup works as expected. What appears to be strange is, that small packets up to 8 bytes are not corrupted but the larger ones do. Maybe in Decnet11MP, the small packets are totally preconfigured in the software program with crc inclusive and the KG11 is then bypassed effectively, bu, that should have to be verified. At least the combination KG11 and Decnet11MP KG11 support is

So Simh Dup works in software Ddcmp packet generation, but the Simh KG11 seem to generate bad checksums and/or checks. For the Pdp8A, I have a functioning KG8 simulation that works in Rts-8, so there is a test reference to fall back on. So I admit and confirm that basic Dup in simh software wise between Pdp11's and with various counterparts (DMC) indeed works, which would make it serve as a base for other sync line implementations like DP8-E(A).