Re: [CAD_CAM_EDM_DRO] Hp 7475 Plotter Servo's

Don't forget: It also flips data receive and transmit (pins 2 and 3).

Try this: using a digital voltmeter, measure the voltage at pins 2 and 3
using pin 7 as a reference. The one with an active negative voltage
(between -5 and -15 volts) is the pin the device is using to send data out
to the world. On your plotter and on your computer (use a 9-pin to 25-pin
convertor if necessary), they must be on different pins to communicate.
Then apply jumpering if necessary, to satisfy the RTS/CTS and DSR/DTR/DCD
requirements of each end.

Realize also that some interfaces actually USE the other control signals to
throttle data flow so as to not overwhelm buffers. Not all use the
character-based throttling, like XON/XOFF and the like.

More details if you need....

Tom Harrison
At 9/29/2005 02:50 PM, you wrote:

>Victor,
>
>The null modem adapter basically puts a jumper between RTS and CTS (pins 4 &
>5) so that the device sees it's OK to send data when it asks for permission.
>In addition, it jumpers pins 6,8 and 20 to provide the required signals for
>the two devices to recognize that they are both turned on. it shouldn't
>matter wich end of the cable that you put the adapter as long as your serial
>cable has all the lines required going straight through. You need pins 2&3
>(recieve & transmit), 4&5 (request to send and clear to send), 6 (data set
>ready), 7 (ground), 8 (carrier detect) and 20 (data terminal ready).
>
>If the device were "dumb" you could use only 2,3 and 7 and it would work.
>However on newer "smart" devices, the computer won't send data if dtr is
>not high and the device may not send back if it doesnt see a high on CTS,
>etc. etc.
>
>IIRC, I have had problems using the com port under XP - seems Microstupid
>decided to keep control of the ports (because they could, and of course,
>they know better than we mortals).
>
>Hope this gives some help.
>
>George
>
>
>
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