macOS RS232 through USB port in Cocoa

Are you using some sort of USB-serial dongle here?

Try the bottom of http://www.keyspan.com/downloads/ for some sample code.

I'm interested in this as well. The next major area of work on the app I'm developing is going to be serial communications with external devices. I'm not there yet, but I'm interested to hear about your results. FWIW, there are definitely other programs out there that use RS-232 under OS X, because I've used at least two of them. I have a Keyspan USB->RS-232/Parallel adapter that works well in OS X.

It seems to me that the easiest way to "talk" to a USB device is to emulate a RS-232 serial port and talk to that.

You can get tons of free (schematic/parts list) to pre-made self-contained circuits pre-programmed out on the Internets.

Programming to them, however, requires use of the naked I/OKit interfaces. For some reason Apple went old-school for its hardware-accessing interfaces in OS X instead of the nicely abstracted, friendly, high-level APIs, such as Comm Toolbox and Input Manager on Mac OS 9 (Classic).

I am sure there is Apple sample code for talking to the modem or something, because I built an app (and Unix daemon) ages ago for OS X that talks to an LCD device via an emulated RS-232 port using I/OKit.

http://developer.apple.com/samplecode/

FireArse said:

This is most interesting. Yes, after the first reply - I noticed the keyspan usb interface...very interesting. Bit pricey though, for what they are. Still. Would be pretty neat.

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I have one that I used to use to update my GPS from Virtual PC. I no longer do this! It works really well. The biggest issue I can see with this is working out what the serial port is called. When you connect the device a serial port is created in /dev but it's name is not predictable as it varies depending on the port it's plugged into!

If you are somewhere in the UK I could lend you the one I have as I don't currently need it...

OK looks like the drivers have changed a little now. The serial port is predicable. When the device is connected you can see these files in /dev:

crw-rw-rw- 1 root wheel 10, 12 Nov 2 17:00 tty.KeySerial1
crw-rw-rw- 1 root wheel 10, 14 Nov 2 17:00 tty.USA19QW3d1P1.1

You should be able to simply write to these to write to the serial port...

robbieduncan said:

OK looks like the drivers have changed a little now. The serial port is predicable.

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Yup, the device nodes are predictable. The original poster can just drop down into c and use iotcl() to read/write the serial port. Example code can be found in the minicom and/or pilot-link open source programs. Both of these programs access the serial device through the /dev device node and function correctly on OS X with USB->Serial dongles.

Python has a nice, simple serial API (which you can call from your Cocoa app probably using NSTask or other method) called pySerial. The serial code from Apple I glanced at a few years ago looked pretty complex and low-level. I've done a bunch of C stuff with QuickTime and CoreAudio, but this stuff made my head hurt. By contrast, pySerial was very easy to understand and use.

There is Cocoa Dev House London. I've signed up but never been. Other than that if you organise something I'm sure a few people would go along. I'm in London and would come if I'm around. I'm hardly a professional Mac developer though!

mduser63 said:

I'm interested in this as well. The next major area of work on the app I'm developing is going to be serial communications with external devices. I'm not there yet, but I'm interested to hear about your results. FWIW, there are definitely other programs out there that use RS-232 under OS X, because I've used at least two of them. I have a Keyspan USB->RS-232/Parallel adapter that works well in OS X.

Click to expand...

Check http://www.harmless.de/cocoa.html for his AMSerialPort class.. Allows you to easily use the serial port(USB adapter) with Cocoa.