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Serial console on the Actiontec
With a little research, I was able to determine that the Actiontec came with a serial console, and that hooking up to it was fairly simple. The only catch was that it used 3.3 volt logic (most serial adapters use much more than that).
An associated resource noted that 3.3-volt line levels are terribly common in devices such as cell phones, and USB-to-serial cables designed for these phones are easy to come by. I went to my local radio shack, and picked up a serial data cable for the LG 1200; not because it was the cheapest option available, but because the important details were already available on the site, and I knew it would work.
Wireup details
To take apart the Actiontec, you just have to remove the 4 screws found
underneath each of the rubber feet. Once disassembled, you'll see something
similar to this picture. Note that the first serial console is attached
to the set of pins on the right side. The only pins we're worried about are
Ground, Transmit, and Receive. Those are the first three pins in the set
(reading left-to-right).
Also worth noting is that Actiontec left easy-to-use pins, rather than
simple solder points like some other companies do on their production
devices.
In fact, these pins use the standard size and spacing found
on most computer boards, so connectors are easy to come by. For example,
this connector used to connect the audio output of
a CD-ROM drive to the sound card. I only need three of the four wires,
but it will do just fine.
It's important to me that my connection to the modem be reliable,
since I don't want to have to re-open the box because a lead came loose.
At the same time, I don't want to solder anything: the modem's not mine:
it belongs to Qwest. So when I'm done, I need to be able to remove
everything and leave no trace of intrusion. Hence, the audio cable
connector plan.
Obviously I can't punch any new holes in the case, and the only holes
large enough to fit this kind of wiring are the ones in the bottom where
you would mount the box on a wall or something. So, using a high-tech
connector detaching device (which I know looks deceptively like a rusty
old safety pin), I remove the connectors from "outside" end of the cable,
and in fact re-arrange the order on the wires on the "inside" connector.
I feed one end of the cable through the hole in the bottom of the case,
and connect the other end to th appropriate pins. In the picture, I have
one of the black cables taped over--that's the one that's connected
to the fourth pin, the one that I wasn't using. I eventually just removed
it altogether.
Serial cable
All that remained was to attach up the serial-USB cable and see how it works. I chopped off the connector that went to the cell phone and picked out the wires I was interested in. For this particular model, the red wire went to Receive, the orange to Transmit, and the shielding was the ground. I had gleaned that information from this page, the same page that told me which cable to buy.
The USB-serial adapter I bought is based on the Prolific PL2303 chipset. In order to use it with Windows, you need drivers that you can find on the Prolific support site. I'd read that the Linux drivers shipped with the kernel, but I wasn't able to make it work, even after an extensive five-minute trial.
Once you wire it up, the appropriate connection settings are 38400 8-N-1. Remeber that hardware flow control isn't available, because you didn't use those wires. I just left flow control off, and with good results.
After testing to make sure everything worked (and I got a console
over the serial terminal), I soldered the wires together, insulated
them with black tape, and then taped the thing up. The finished
product looks very reasonable.
Now that I've got working console, I can go ahead and try to figure out what went wrong with my firmware upgrade.