RS-232 IRQ etc

[Neil McGuire]

I’m trying to use the external DE-9 connector to communicate with an external device, using only pins 2 (TX), 3(RX) and 5(GND). I tried using setserial to see what IRQ and Port were being used, and it returned UART undefined, port 0x0000 and IRQ 7. Is that right?

The application I am using opens a boost serial_port on /dev/ttyS2, like the manual says, but no data seems to make it out, nor in. It works fine on /dev/ttyS0 on my ubuntu dev box, but not on the CDP. Are there any utilities/conf files I need to look at to try to figure out what the port and IRQ should be set for?

[Jesse Gilles]

You don’t need to specify the port and IRQ, you should just need to use /dev/ttyS2 (it is already configured with the correct hardware info). I would recommend running microcom on the port with the correct baud rate and confirm that you can send data back and forth?

[Neil McGuire]

Okay, I took a break from it for a while and have come back to it.

I have minicom on both the CDP and my development pc. When I hook the target serial cable into the dev pc, I get the expected data. I then plug the cable into the cdp box, and get nothing. If I hook the serial cables (with a liberal number of gender changes) directly from the cdp box to the dev pc, I can pass data across between the two of them.

Here’s the settings I have that allow them to talk to each other and for the dev pc to read from the signal source, which is a three-wire (gnd, rx, tx) connection:

Development PC:

Serial Device: /dev/ttyS0

Lock File: /var/lock

Callin Program:

Callout Program:

Bps/Par/Bits: 9600 8N1

Hardware Flow Control: No

Software Flow Control: No

CDP box:

Serial Device: /dev/ttyS2

Lock File: /var/lock

Callin Program:

Callout Program:

Bps/Par/Bits: 9600 8N1

Hardware Flow Control: No

Software Flow Control: No

I was wondering if the driver was expecting there to be more than the three pins active? I’m also going to try a USB to Serial converter, but am not sure what device that would end up being.

[Neil McGuire]

Alright, got the USB Serial port up and running, reading just fine from the source. I just had to modify defconf in /openembedded/recipes/linux/[version used] to enable the PL2303 driver, and it got up and running as ttyUSB0. Still not sure why the built-in RS232 can’t read the source.

[Jesse Gilles]

The external RS232 port is setup to be a DCE port, so the RX and TX lines are swapped compared to your PC serial port (DTE). You’ll need to use a null modem adapter when you’re connecting the serial device to the CDP since the CDP is DCE and your external device is also DCE.

[Neil McGuire]

I re-soldered the wire swapping RX and TX, and it’s working now. Thanks, Jesse.

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