William L. Maltby wrote:
On Thu, 2009-02-26 at 14:29 -0600, Robert wrote:
<snip>
breakout box. Lacking one of those, you might find the statserial program to be of some use in figuring out what the control lines are doing. # yum --enablerepo=dag install statserial will install it. It has a short man page. Run with no options except device ( # statserial /dev/ttyS0 ) will cause it to loop, indicating status of all control signals. You can manually tweak any of the pins with direction of "in" with a 9-volt battery or by using a paper-clip
IIRC (very iffy) +/- 12 volts is needed.
jumper from one of the "out" lines. It won't be long before you can identify the port, moving an "unknown" to "found".
There are pins designated to _provide_ the correct voltage full time (on 25 pin units - unsure about 9 pin). The google will get a specification of which they are - I can't remember.
The RS-232C (un) standard specifies +5vdc to +25vdc as a "space" on data lines and a "true" on control lines; -5vdc to -25vdc as "mark" and "false". -5 to +5 is undefined ---BUT--- how many times have I seen the damn things operated using ttl levels. DTR (pin 4 of 9 or pin 20 of 25) should be a logical 1 if the port has been initialized.