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Tube❄️Time

this is an indirect jump to the console output routine. it's supposed to beep. but it's jumping to 0000! on initial boot, A600 etc is supposed to alias to 8F80 which is in ROM.

20 comments
Tube❄️Time

the jump table is getting copied into the 6532 RIOT but the write is getting corrupted. it's supposed to be '89' but something else is trying to drive the bus at the same time

Tube❄️Time

thanks to the magic of the 16822 logic analyzer trigger output, I can see that the 6532's R/W# never gets driven low.

bitsavers.org

@tubetime
I should see if we have the schematic and run it through the blueprint scanner

6532 section of the SYM-1 schematic
William D. Jones

@tubetime If I had enough $, I'd design a Super-RIIOT IC (SPI Ultra Precision Extra ROM ROM I2C I/O Timer... acronym needs work)

Tube❄️Time

U9 pin 11, aka Memory Write Protect#, measures 30 ohms to ground. this is suspicious.

Tube❄️Time

sure enough, bad inverter. looks like it was bad back in the day--someone removed the MM to 45 jumper.

Tube❄️Time replied to Tube❄️Time

now it beeps and the display lights up! it's alive.

Sergio Aguayo replied to Tube❄️Time

@tubetime What would've been the purpose of the MM to 45 jumper then?

Tube❄️Time replied to Sergio

@sergioaguayogr the memory in the 6532 is used as a vector table. it's nice to protect it from accidental modification by a runaway program, so MM to 45 is a write protect function.

Tube❄️Time replied to Tube❄️Time

seems to be a similar issue. when it tries to jump to outvec+1 (previously stored in the 6532's RAM) it goes to 0000 instead of the actual character output routine

Tube❄️Time replied to Tube❄️Time

pin 11 of this inverter is shorted to ground. this is the exact same problem as the last SYM-1!

Tube❄️Time replied to Tube❄️Time

so strange. different manufacturers and exactly the same failure (~20 ohm short from pin 11 to ground). must be damage caused by something the last owner did.

bitsavers.org replied to Tube❄️Time

@tubetime

woot!
at one point I had a SYM/KTM. The editior/assembler firmware is under bitsavers.org/pdf/synertek/sym

Joviko Wi replied to Tube❄️Time

@tubetime

Redid the sketchy solder on R83 too. Nice!

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