"The OP said he was working with code for a model 20." That was only barely a true S360 and had a few instructions peculiar to it."
Yes. XIO is the I/O instruction that reads or writes. Like other 360's, I/O is asynchronous. You have to test (with TIOB) to see if it is done yet. With 8K core, half the core is available without a base register. As I understand it, many were only 4K. It does have some fairly complex instructions, such as DP, ED, and TR, and leaves out some simple ones like L and LR. Registers are 16 bits, so LH, AH, SH, CH, and STH are there. AR and SR, but not most of the other RR instructions. PACK, UNPK, MVO, ZAP, AP, SP, CP, MP, DP so full decimal arithmetic. MVI, MVN, MVZ, CLI, MVC, CLC, NI, OI, ED, BR, B, BASR, BAS. and then the model 20 specific: XIO, TIOB, HPR, SPSW. -- glen
