I was writing a routine to break out DAP flag bits to aid debugging when I noticed a possible discrepancy between DAP V5.6 and Tops-20, viz:

DAP Bit	Bit Meaning	PDP-10 Bit	Tops-20 DAP Symbol
0	Stream Identification Field Present	1B35	HD$SID
1	Length Field Present	1B34	HD$LEN
2	Extended Length Field Present	1B33	HD$LN2
3	Bit Count Field Present	1B32	HD$BCT
4	Reserved	1B31	HD$SEG
5	System Specific Field Present	1B30
6	Not last message of segmented message	1B28

DAP V5.6 reserves bit 4 and defines bit 6 to flag that a segmented message is being sent and that this is not the last message.  In other words, that there will be another message.  Tops-20 is using bit 4 for this purpose and by rights it would appear that it should be using bit 6.

I will go see if I can't scare up what Tops-10 is doing, but I was wondering if anyone knew what other OS's are doing.