Re: [CAD_CAM_EDM_DRO] Hp 7475 Plotter Servo's

Victor A. Estes wrote:

>Tom H.,
> I have negative voltage coming off of pin 3 of the computer's com1 port.
>But I'm not convinced that the computer is sending out any data from the
>com1 port. When I send a sting of commands through the port using DOS, I
>did not get any change in the voltage across the pin. In fact when I send
>the string, my curser hangs up and does not let me type any more commands
>without first exiting the DOS window and then opening back up and starting
>over.
>
>

Try using HyperTerminal. You can cut/paste text into it if you want to
send data quickly. If you were opening the port with ",p" at the end,
try not doing that - it turns on XON/XOFF handshaking, which you don't
want for testing purposes. You should use something like "mode
COM1:9600,N,8,1".
-12V is correct for the "mark" state = logic 1, +12 for "space" = logic
0 (unless I've got them backwards :) ). The port should be toggling
rapidly (depending on the baud rate) between -12 and +12 V. You won't
be able to see it on a multimeter, you need a scope for that. What you
may be able to do is pick some character that has 4 bits on and 4 off
(try "f" - make sure it's lower case - that's 01100110 binary), and see
if you get a DC voltage near 0.
You could also try setting it to 110 baud, and put the meter on AC -
sending 'f' characters at 110 baud would give something close enough to
60 Hz to be detectable.

> I think at this point I am going to try and find a DOS only computer (No
>Windows) laying around and try it.
>
> Still trying to get the plotter to work.
>
>Victor A
>

Good luck with that
- Steve