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power.txt
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1996-07-14
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61 lines
Receive Interface Power
-----------------------
The receive interface uses these pins of the serial port.
Signal 25 pin 9 pin
Name connector connector Function
------ --------- --------- --------
TxD 2 3 * see below
RTS 4 7 *
DTR 20 4 *
GND 7 5 ground
DSR 6 6 amplified audio to computer
Notice that the serial port has three output lines (TxD, RTS,
and DTR) which are used to power the op amp, and in some cases,
provide audio output and push-to-talk (PTT).
Different interfaces use different combinations and polarities
for the power.
Power taken from
----------------
TxD RTS DTR Interface
--- --- --- ----------
+ - SSC PC SSTV
+ - AEA FAX
+ - EZ SSTV (version 2)
- + SSTV Explorer
- + VESTER
- + HAMCOMM
- + JVFAX
- + MSCAN
- + GSH-PC
Note that the earlier systems used the RTS pin for positive (+)
power and either DTR or TxD for negative (-).
Most later systems have settled on DTR for positive (+). This
is the default for EZ SSTV version 3 but the polarity can be
reversed for use with the older interfaces.
To change the polarity, pick "SSTV Interface" from the "Setup"
menu, then click on the "Power" button.
What happens if it is set wrong?
1. Circuits with the transmitter's push-to-talk (PTT) activated
by the RTS or DTR will turn on the transmitter when the
program is in receive mode.
2. An attempt to receive will result in a message that there
is no receive interface or audio present. This is because
the interface is not receiving the necessary power to
amplify the audio and apply it to the computer's serial
port.