> And I read somewhere that signal levels on the newer RS-232-C port lines are more
> conforming to the RS-232-C standard and pose more problems to BayCom like
> modems. This specially affects RX.
My usual experience of this is the MC1488 and MC1489 line drives on a
serial card
seem to work whereas the older type (like found on an orginal IBM PC/XT
async card
(can't remember the numbers)) tx but don't rx.
The problem is that the 1488/1489 accepts 0v as -ve and +5v as +ve
whereas the
older line drivers see 0v & +5v both as +ve (so you get no transitions
on the TTL
side of the line driver into the UART).
Solutions
1) Bung a power steering diode to collect some juice off the serial port
lower than
0v and then add a small circuit to the data out of the modem board to
get output to
swing down.
2) Add a MAX232/ICL232 etc to get the correct output but this'll need an
additional
power supply.
J