Hey serial-knowing friends: are all RS232 DB25 pinouts the same? Are any two DB9-to-DB25 adapters going to be identical? I have a DB25-equipped serial device I’m getting a USB interface for, but looks like most USB interfaces only come in DB9 flavour.


@misty 1) No they're not all the same, but effectively yes. It is possible, however, that not all DB-25-using devices have all of the pins hooked up; in fact, _most_ have no more than about half a dozen pins hooked up. Older devices sometimes do very strange things, but if it's after the mid 70s I doubt you'll see that.

2) The only difference might be whether the adapter connects the common hardware handshaking lines or not. Most will. Some will connect _only_ pins 2 & 3 and ground.

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@misty TL;DR: There's a very high probability that any two serial ports will plug together with "standard" cables and adapters, the only _likely_ bugaboo is if one end requires hardware handshaking and either the cable or the other end does not support it. You can sometimes "fix" this with some creative jumpering.

@elb Thank you so much! This is really helpful. I found a copy of the pinout for my device, which specifies that it does use the handshaking signals and not just the data pins/ground, so I’ll need to make sure whatever I buy supports that.

@misty in particular if you want to use a USB serial adapter you'll need to verify that it has hardware handshaking. The physical 9 to 25 pin adapter is _probably_ fine.

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