5 Jan
2008
5 Jan
'08
6:35 a.m.
My point was that you'd checked that the TxD line
from the Z80-DART had
got to the 1488, but you didn't say what happened to the other input of
that bit of the 1488, if indeed there is a second input (the TxD could be
using the single-input part of the 1488, of course). If case (3) applies,
you could have had a problem in the logic that drives the other input,
for example.
The other input to the 1488 is coming from pin 17 on the DART which is
marked "RTSA" on the schematic for the DART - the output from that section
of the 1488 goes to the "HSO" or "Hand Shake Out" line on the board
connector - this appears to correspond to pin 20 on the RS-232 connector.
Now as for (2), check there's +12V and -12V
on the right pins of the
1488. And that the ground pin is, indeed, groudned. Remember a supply
might be misisng because osmething is overloading it. Maybe a 1488 or a
dcoupling capacitor has shorted.
It's showing -0.60v for all the -12v test points.