No, nothing happens. What power supply do you mean? the one of the=20
puncher, yes i think it's ok, cuz as I push one of the buttons of the=20
Yes, the PSU inside the punch. Many of use have discovered the hard way
that elecrronic stuff doesn't work unless it's getting the right power,
and that PSU problems are common (I am one of the ones who has spent a
long time tracking down nasty faults before realising the PSU is not
doing what it should be...)
puncher (the tiny holes puncher and the all holes
puncher) it does what=20
it's intended to do.
That sounds as though it's working properly, though.
Well, i tried multiple setups, i don't really remember what i did try.=20
About the null modem cable, I wired as follows:
20 DTR - 6 DSR (puncher - puncher)
3 RD (puncher) - 3 TD (PC)
7 Gnd - 5 Gnd
4 DTR - 6 DSR (PC - PC)
Note that I didn't try the TX from puncher side, cuz I think it's not=20
returning useful data.
Right now, i hooked a led and a resistor to the TX of the PC, I see it=20
flashing as i send some data, then I'll assume the PC is correctly sendin=
Something comes to my mind, I remember from the days that I programmed=20
PIC MCUs that the serial port of a laptop operates at low voltages, 3V I=20
Any port that claims to be RS232 compatable should send <-3V for one
state and >+3V for the other. Most desktop machines swing between =112V
and +12V, I am told some laptops have a much smaller swing than this (but
my _ancient_ laptops generally use -12V and +12V). But anyway....
think. Can it be the problem here? But according to
of the manufacturer, the puncher deals with 3V communication.
Most RS232 devices of that sort of vintage use a 1489 receiver (or a
75189 which is much the same thing). This chip will take -ve input
voltage sithoug damage, but it has a single threshold of IIRC, a little
over 1V. That is, a swing from 0V to 3V would be OK. So wouid -3V to
+3V, Or -12V to +12V. I shouldn't say this, but you can feed a TTL level
signal into such a receiver chip and expect it to work. I've done this a
few times fro testing, I would enver do it on a deviec that was to be
used by someone else.
What I would do next is a little conection-tracing inside the punch.
Where does the RxD (data input pin (3?) on the DB25 connector) go? Can
you trace it to an RS232 receiver chip like a 1489?
If you have a logic probe or 'scope, does the output of the appropriate
section of this receiver change state when you send data to the punch?
Is ther a recognisable serial chip? Either a 'dumb' 40 pin UART, like a
6402 or a microprocessor bus chip (6850, 6551, Z80-SIO, 8250, 8251, etc).
If you can find one, is the serial input (receiver input, whatever) pin
of that changing state when you send data from the PC? If not, what is
between the line receiver and the serial chip? Maybe some jumpers to
select a currnet loop interface (as others have suggested).