Parallel port

[kodak80]

Hi everyone

I tried using PARCP on my 2nd board and it fails to work which may mean either I have some dodgy soldering or the port pins are not correct.

IMG_2010[1].JPG

[rpineau]

Interesting. the data is only off by 1 bit : $4853 expected but it got $5853

Code: Select all

$4853 : 0100 1000 0101 0011
$5853 : 0101 1000 0101 0011
wrong bit -|

So check the 6th bit (IOB5) on the parallel port between the 2149 and the connector.
Looks like the bit is stuck to 1 so may be a short with VCC.

[kodak80]

I have tested continuity with a multi-meter on the 2149 between pin 8 (IOB5) and pin 40 (VCC) on both of my boards and it looks like they are connected.

I cannot see any obvious soldering shorts.

I am guessing that they shouldn't be?

Reading the data sheet for the 2149, the IO bus pins have a pull-up resistance, so does this mean they are indeed connected to VCC?

I have also tested continuity to pin 7 on the parallel port and its connected to the 2149 pin 8.

[exxos]

There are some vias close to the parallel port pins.. so worth checking you haven't bridged over to any.. also possible the YM chip is faulty ?

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[kodak80]

I have swapped the 2149 chip and same results so not the chip.

All IOB pins on the 2149 chip are showing as connected to VCC when I do a continuity check with my multi-meter. Not sure how a soldering short would connect all IOB pins to VCC?

Also, not sure how I would have made this happen on 2 boards.

[exxos]

I never checked that chip with the meter before,so I don't know if that is right or not anyway.I would suggest you check on a normal ST,and also suggest you use resistance setting on your meter rather than continuity test.

[PaulJ]

I don't have anything real to connect to the parallel port but mine was questionable when I ran it with the diag kit. With just the test board connected it failed but when I hooked up the digital analyzer it started passing which I attributed to a real device having pull-ups. I also changed the 2149 and no difference. Maybe I'll give it another run today. The Diag test walked 1 across the eight bits reading back what it had written.

[exxos]

Maybe try a 10k pull up on the io pins and see if that helps ?

[PaulJ]

I'll take a look today and see if I can get to reliable operation with the cart.