I am trying to use the serial ports on my TS-7300.
I am running the latest Debian Linux from TS with the 2.4 kernel,
which presumably has the standard FPGA configuration.
As I understand the manual, COM ports 3 through 6 are not
RS-232-compatible; instead they use logic levels. I tried wiring up
some chips to them and had some problems, so I took out my trusty
oscilloscope to look at the voltage levels on the pins.
First off, I made sure I was reading the pin numbers correctly, since
TS uses non-standard numbering. The pin closest to the white dot on
the circuit board is pin 1, the one next to it is pin 2, and so on
through pin 5. On the other side of the connector, opposite pin 1 is
pin 6, and so on. Do I have that all correct?
I attached the ground of my scope to the ground of the incoming power
supply, where it attaches to the board. Testing pin 5 of COM3 shows
zero volts, which is correct because it is the ground pin of that
connector.
But if I look at pin 3, which is serial out, I see a constant -5 volts
with about a 0.5 volt sawtooth wave superimposed on it. This is right
after booting up, before I run any programs myself. If I then open
this port in Kermit and send some data at 9600 baud, the voltage shows
a series of pulses to +5 volts. Each pulse is a multiple of about 500
usec., which is the bit time at 9600 baud.
OK, I know that the serial standard is to output a logic 1 when the
line is idle. So it looks to me like the output of COM3 is not only
inverted, but using +-5 volts instead of 0 and 5 volts. In fact, it is
like the way RS-232 levels are supposed to work, where the idle
("marking" a.k.a. 1) state is -12 volts or so, and the "space" state
is +12. So am I mis-reading the manual, and COM3 to 6 are actually RS-232?
Finally, the names of the COM ports in Linux do not match what it says
in the manual. COM3 is /dev/ttyT8S0, COM4 is /dev/ttyT9S0, and so on.
Has anyone else seen this behavior?
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