tom (02/11/83)
I've experience only with the Intel and NEC versions, but here goes. Reset doesn't always work? Is the AMD 9551 an 8251 or an 8251A? If it's an 8251A, is it latching in break detect mode? The 8251A seems less likely to do this than the 8251 from my experience, but I've had problems with both. My first suggestion is that 6 Tcy is not enough delay. In some instances the recovery period is 8, 16, even 18 Tcy. I suggest you try delaying about 20 Tcy between writing cmds. I have a few notes and a somewhat dated but useful information sheet which I will be happy to mail to you if you'll send me your U.S. mail address. My address is Tom Holland, M.S. #96 GenRad Rt. 117 Bolton, Mass. 01740