OS X 10.6 + Airport Express + Keyspan USB to serial adapter = Imagewriter?

You can either re-draw the diagram in mirror image, keeping the pin numbers in the same orientation, or re-draw the pin numbers, keeping the diagram in the same orientation.

The pins in Table 4 have the correct names associated with the pin numbers. I listed what Inside Macintosh says somewhere above, and it does correspond to the table 4 signal names.

RS 422/3 uses "push/pull" or "double rail" logic. Inputs to these devices will attempt to read the difference between their - and + leads as the signal.

To convert from RS422/3 to RS232, the mantra is:
"Open + on Driver,
Ground + on Receiver."

That will mean you are looking at the difference between RxD- and sGnd as your input signal, which will work fine. NOT doing that will leave you looking at the difference between RxD- and float, which may not work very well.

John Galt wrote:
Success! Here is a diagram of the working cable (color codes for internal reference only):

Glad to hear it.

As expected I can't find a way to make the Imagewriter work using the Express USB port.

With the adapter plugged into the Express USB port, did you see if it was listed in /dev? In the Terminal, you could do

<pre style="overflow: auto;font-size:small; font-family: Monaco, 'Courier New', Courier, monospace; color: #222; background: #ddd; padding: .3em .8em .3em .8em; font-size: 9px;">ls /dev | grep cu</pre>

and see if anything looking like cu.KeySerial1 or cu.USA19xxxxx shows up. For printing, you use the "cu" or callout devices. It's a long shot. I don't know what you tried and I didn't cover the device URIs used for serial printing in my posts on the OpenPrinting forum.

John Galt wrote:

Matt Broughton wrote:
With the adapter plugged into the Express USB port, did you see if it was listed in /dev?

Well, here's what the above Terminal command returns *with the adapter plugged into the iMac's USB port:*

cu.KeySerial1
cu.USA19H191P1.1
cu.modem

When you set up a serial printer through the CUPS web interface, you will want to always use the cu.KeySerial or KeySerial device. This is an alias to the first Keyspan serial port on the Keyspan device. In your case, there is only one port on the device.

The cu.USA19H191P1.1 address will change as you change USB ports. If you use this device URI when you set up a serial printer, you will lose contact with the printer if you plug the Keyspan adapter into another USB port.

But when it's plugged into the *Express USB port* I only get

cu.modem

This means that the system does not see the Keyspan serial ports when it is connected to the Express USB port. The cu.modem would be the port on your computer for your modem. I suspect that there will always be a cu.modem listing whether or not you actually have a modem installed. Perhaps there is some sort of vestige modem port on the mother board.

Of course Airport Utility doesn't report any USB printers connected to the Express, nor can I find a way using Printer Setup to make it work as a remote printer (such as specifying the Express's IP address).

You've piqued my interest. What does this mean?

I don't know the technical explanation, but it means that you will not be able use the serial port through the Airport Express. I'm not sure if this is a limitation of the Keyspan kernel extension or a limitation of trying to do serial communications over Ethernet.

Also, there is no way to directly access a USB port in Mac OS X. Under most Linux distros, you would find USB ports listed under the /dev listing. At least that is the way it used to be. I haven't checked in quite some time.

You also have to remember that Printer Setup Utility will never be able to see a printer on a serial port. It will show the printer and its status once it is added, but that's about it. Printer Setup Utility is Apple's GUI for the printing system. Since Apple dropped support for serial devices a long time ago, it stands to reason that they would not support the use of serial printers. Luckily, CUPS is open source and has maintained support for serial devices. The serial backend must be compiled from source code and manually added as a backend in Mac OS X. The Imagewriter software does install such a serial backend. I think the serial backend the the Imagewriter software package installs will work for OS X 10.2.x through OS X 10.5.x. For OS X 10.6, you will need to add the serial backend I have on my website http://webpages.charter.net/mbroughtn/serial_printing.html.

John Galt wrote:
Could you explain what the serial backend is intended to accomplish, that is not already implemented with Ghostscript and the imagewriter-foomatic driver? The latest version of Ghostscript is supposed to work with OS X 10.6, of course I don't have it yet.

The CUPS printing system is a modular system. In the simplest terms, it can be thought of as having a front end and a backend. The front end prepares the print job and puts it in a format that your printer can understand. That is what the Imagewriter PPD, the cupsomatic [1] program Ghostscript do.

The backend provides the communications with the printer. The serial backend uses the file that the front end prepares and provides communications between the host computer and the serial printer for the print job. Each protocol has its own backend such as serial, USB, JetDirect, lpd, ipp, etc.

I see that your Serial Print Enabler allows changing baud rate etc. which I was wondering about. What other benefits does it confer?

The Serial Print Enabler on my website is not something I wrote. It is only the serial backend that is derived from compiling the CUPS source code. The CUPS source code contains various backends. Apple has chosen not to provide the serial or parallel backends to OS X users when it installs the CUPS printing system. I only go back to the source code, compile it to get the serial backend, and then package it for others to add to their systems.

To communicate with any serial device, one must on specify certain parameters such as the baud rate, parity, and flow control. Both ends of the serial communication must use the same parameters or the communication will fail.

The only benefit that the Serial Print Enabler provides is that it installs a piece of software from the CUPS package that Apple does not include in OS X.

In other words, will I need the serial backend for Snow Leopard, and why?

You only need a serial backend for the computer that will be the host for the Imagewriter. That is the only computer that will be communicating directly with the printer. Computers that used the shared Imagewriter on the host computer only need to communicate with the host computer.

I am reluctant to install it on my iMac lest in conflict with drivers that already work. I admit to some confusion as to how Ghostscript functions - the ease with which it installs and operates is a testament to its developers.

I know of no conflicts with any other drivers.

Speaking of which, is anyone working on a solution for an Express USB connection? Would it require proprietary information known only to Apple?

I have no idea.

... Perhaps there is some sort of vestige modem port on the mother board.

🙂 There really is a modem. The desktop I'm doing my experimenting with is an iMac DV SE, but I generally connect via dialup using my AirPort Extreme's dialup modem. Broadband has yet to arrive in Galt's Gulch, another reason for retaining some of my aging equipment, since Apple abandoned dialup users ages ago. I even keep a spare Extreme with modem, just in case.

You will find the cu.modem entry in /dev even on computers that have no modem.

Now for the "why didn't I think of that before" idea. If you are planning on using a pre OS X 10.6 computer to host the Imagewriter, I don't think you even need to go the serial printer route. You can have a computer running OS X 10.4.x or OS X 10.5.x that has the Imagewriter connected via AppleTalk and still share that printer with a computer running OS X 10.6.x. All that is needed is that the host computer be able to communicate with the printer.

[1] cupsomatic is the forerunner of the foomatic-rip program.

John Galt wrote:

The only benefit that the Serial Print Enabler provides is that it installs a piece of software from the CUPS package that Apple does not include in OS X.

Good information Matt, thanks. I'll install the Serial Print Enabler; I don't think I'll need it but it sounds like it won't hurt.

There is only one file installed - /usr/libexec/cups/backend/serial. The download also includes an uninstaller in case you ever want to get rid of it. Just be sure to install the Imagewriter software first. That package installs a serial backend that will not work in Snow Leopard. The Serial Print Enabler will backup and replace any serial backend it finds installed.

Of course the Imagewriter is serial only, an even rarer breed of printer. I am wondering if a serial print server, similar to the parallel print server I bought, assuming I can find such a thing, will work with the CUPS interface.

I understand the challenges involved with cabling and configuring the print server itself, but I'm encouraged by this success getting the Imagewriter to work with the Keyspan adapter. Would you care to speculate on the chances of success with such a device?

I tried Googling for serial print servers. The results that turned up do not look promising. I kept running into statements such as "will only work with PostScript printers", "will present the printer as a LaserWriter", and "57600 baud rate". I gave up after about 15 minutes. That doesn't mean that there isn't a product that would work. I think it will be a tough go to find a serial print server that will work at 9600 baud with a QuickDraw printer.

Those certainly seem more promising. I feel a good print server should be able to be configured from a web browser ( personal opinion). In any event, I just don't feel comfortable with any sort of conjecture as to whether they would work. My knowledge just is not deep enough.