Yes, there are a series of bits in SSR0 to indicate the particular error: 'non-resident', 'length', 'read-only', etc (and also the segment number the error's from). As my message mentioned, we're seeing the 'length' error bit on, and for segment 1 (which the instruction isn't using). Fritz does have a spare board, but it has known errors. We haven't thought about borrowing one yet, it may come to that. Well, _some_ of it could. E.g. if the 'jsr r5, csv' is read as 'jsr r4, csv', dropping the '1' bit in the register number, that would explain the wonky R5 content - R4 does contain the 034 that should be in R5, I have just noticed. But that doesn't explain the bogus MM trap. Although I suppose there could be several different problems, all at the same time. Nope. Noel