[For once I did not crosspost and now PDP-8 Lovers list is not working right, so it goes to classiccmp again.] Hi, after dishwashing I reassembled my "new" PDP8/A and it's working again, after David Gesswein hinted me to the programmers console quick reference, I was able to enter my first manually assembled programs and it's indeed working! I must say that I never thought I would ever manually assemble a machine program, but with the PDP8 it's remarkably easy. My first PDP-8 program is a memory test, and I was glad I did it because I found a problem. My test goes through all memory fields and writes into each cell its address in the field. Then it reads that address out of each field again and so finds problems. I have 3 16k words boards and one 8k word board. Two of the 16k boards are good but both seem to want to play the role of the lower fields 0 to 3. The third 16k board plays the high fields 4 to 7, but it has a systematic error masking out bits 6 and 7. All data X I write into it is read as X AND 7717. The 8k board has a similar bit mask error, it's mask is 6777. Is this a fatal problem or can one fix it by cleaning some contacts or redo some crummy soldering? I assume the core mats are all fine, because they would not just lose a few columns of data bits, right? I also assume that others had to deal with similar issues, because apparently such errors are not uncommon. What's the trick? (I did swap them into various backplane slots, just to make sure it's not just a gap in the data bus lines. ... BTW, does the OMNIBUS need something like grant continuity cards for intermittent empty slots?) thanks for your advice, -Gunther PS, just to show off (and to save this stuff from my hand- written notes) here's my program. It's ugly spaghetti code with quirks because I had to modify it at the console (remember: never start coding without having done your work on paper :-) I now understand much better :-) I'm not sure I have the symbolic assembly language right, I may use some things (like the Z modifier for zero-page addressing) that is not standard but helps me code right. 0020 0000 LOC , 0 TESTED MEMORY LOCATION 0021 0000 FLD , 0 TESTED FIELD NUMBER WRITE LOOP 0200 7200 CLA A = 0 0201 1254 TAD FLDINI A += FLDINI 0202 3021 DCA Z FLD FLD = A; A = 0 0203 1257 TAD LOCINI A += LOCINI 0204 3020 DCA Z LOC LOC = A; A = 0 0205 1020 WRLOOP, TAD Z LOC A += LOC 0206 3420 DCA IZ LOC *LOC = A; A = 0 0207 2020 ISZ Z LOC IF(++LOC == 0) 0210 5205 JMP WRLOOP ELSE GOTO WRLOOP 0211 4234 IFRET, JMS INCFLD THEN A = INCFLD() 0212 7450 SNA IF(A != 0) 0213 5205 JMP WRLOOP ELSE GOTO WRLOOP /*FALLTHROUGH*/ READ/CHECK LOOP 0214 7200 CLA A = 0 0215 1254 TAD FLDINI A += FLDINI 0216 3021 DCA Z FLD FLD = A; A = 0 0217 1257 TAD LOCINI A += LOCINI 0220 3020 DCA Z LOC LOC = A; A = 0 0221 1020 RDLOOP, TAD Z LOC A += LOC 0222 7041 CIA A = -A 0223 1420 TAD IZ LOC A += *LOC 0224 7440 SZA IF(A != 0) 0225 7402 ERROR, HLT ELSE HALT 0226 2020 ISZ Z LOC THEN IF(++LOC == 0) 0227 5221 JMP RDLOOP ELSE GOTO RDLOOP 0230 4234 JMS INCFLD THEN A = INCFLD() 0231 7450 SNA IF(A != 0) 0232 5221 JMP RDLOOP ELSE GOTO RDLOOP 0233 7402 OK, HLT THEN HALT INCREASE DATA FIELD SUBROUTINE returns 0 if success resets field to 0 and returns -1 if overflow 0234 0000 INCFLD, 0 0235 2021 ISZ Z FLD IF(++FLD == 0) 0236 7300 CLA CLL ELSE { A = 0; L = 0 } 0237 1021 TAD Z FLD THEN A += FLD 0240 7047 CIA A = -A 0241 1255 TAD FLDMAX A += FLDMAX 0242 7510 SPA IF(A >= 0) 0243 5261 JMP RSTFLD ELSE GOTO RSTFLD 0244 7300 CLA CLL THEN { A = 0; L = 0 } 0245 1021 TAD Z FLD A += FLD 0246 7006 RAL 2 A <<= 2 0247 7004 RAL A <<= 1 0250 1260 TAD CDFTMP A += CDFTMP 0251 3252 DCA CDFDO CDFDO = A; A = 0 0252 0000 CDFDO, 0 0253 5634 JMP I INCFLD RETURN INITIALIZATION VALUES 0254 0000 FLDINI, 0 0255 0007 FLDMAX, 7 0256 0257 0300 LOCINI, 0300 0260 6201 CDFTMP, CDF RESET THE MEMORY FIELD BACK TO 0 assert A == -1 0261 7000 RSTFLD, NOP 0262 1254 TAD FLDINI A += FLDINI 0263 3021 DCA Z FLD FLD = A; A = 0 0264 4234 JMS INCFLD A = INCFLD() 0265 7040 CMA A ~= A 0266 5212 JMP IFRET GOTO IFRET -- Gunther Schadow, M.D., Ph.D. gschadow(a)regenstrief.org Medical Information Scientist Regenstrief Institute for Health Care Adjunct Assistant Professor Indiana University School of Medicine tel:1(317)630-7960 http://aurora.regenstrief.org