Serial Woes.

[swestrup]

So, I haven't been able to get the serial IR receiver working on my PVR. It could be any one of a whole host of problems, and I'm trying to narrow things down. First off, I need to know that I'm A) programming the correct serial port (this machine has two, and I don't know which is which) and B) that the serial port I'm using actually works.

My plan was simple: I have an old external 2400-baud modem with auto-adaption capabilities so that if a serial port is even vaguely usable, I can talk to the modem and it can tell me what is up with the port. All I need is to connect it to the machine with an appropriate serial cable, and I'm good to go.

Well, that's my next problem. It seems that I no longer own a serial cable with a male 25-pin end on it. I do have some 25-pin to 9-pin adapters but they're all female-25 to male-9 where I need male-25 to male/female-9 to get things to work. With all the cables and adapters I have this should have been easy to come up with, but I'm surprised to find myself missing crucial bits.

So, before I go out and buy a serial cable adapter that I will only be using for a short time for diagnostic purposes, I thought that I would ask my friends list. So, does anyone have any old serial cables or adapters around that I could use to hook an old serial 25-pin DCE device (modem with female 25-pin connector) to a modern DTE (computer with 9-pin male connector) that I could borrow?

Comments

[skjalm.livejournal.com]

22 and 8 pins? Ehm, the world I grew up in had 25 and 9 pins for serial ports ;)

If you simply need to figure out if it's the correct serial port you could try to connect it with a null modem cable (if you have one) to another computer and start a terminal program (e.g minicom) in either end and see if they can find each other.

An even simpler test would be to put an LED and a resistor in serial from the DTR (or RTS) to ground on the serial port and trying to send anything with minicom or write a simple program that tickles the bits a little. You will probably not be able to see the individual changes, but you should at the very least be able to see it flick on and off once in a while. For the record, a suitable value for the resistor is, oh, 1 kOhm. That should be low enough that it's visible even in daylight and high enough to in no way risk damaging the port. You could probably get by with anything from 2-300 Ohm to a couple of kOhms, but 1k is, well, a nice middle value.

[swestrup]

Nyah! I fixed it while you were writing your comments! This damn cold had me misremembering the number of pins on a standard cable.

[skjalm.livejournal.com]

lol - have you figured out if you've got the correct port?

[swestrup]

No, I just fixed this post. The problem itself remains.

[swestrup]

I'm not a hardware fellow. I do not own any resistors, nor naked LEDs, nor do I have a soldering iron.

I DO have a null-modem cable but its got a female DB-25 on one end, which is precisely the thing I don't have any way to connect to.

[skjalm.livejournal.com]

Ah... well... a cumbersome thing would be to check the motherboard to see which port is physically which and then the bios to check the settings and then /proc or simply checking if you can open each port on the addresses found in the bios...