November 14, 2017

Hacking on a Digital Lightwave ASA-PKG-OC12

I often cruise the "Business and Industrial" categories of eBay looking for things that are 1) cheap 2) interesting and 3) "For Parts or not working". This device seemed to fit all three:

It's some kind of portable computer used to troubleshoot various old high-speed telecommunication links, like T1, SONET, etc.

I thought it would be fun to hack on. Maybe the LCD/touchscreen could be used with a Raspberry Pi or something? What kind of OS would it run?

The device was in pretty sorry shape, and the plastic surround was in tatters (it was cheap). Underneath, though, was a quality aluminum chassis without a dent or scratch.

Contents

Of course I took it apart before turning it on. The insides were somewhat surprising:
  • Three PCBs in a sort-of mezzanine arrangement, containing all of the huge old ICs for the various telecom functions, and about a billion Xilinx PLCC devices, some socketed.
  • The main PCB had the real prize: a Megatel PC/II+ PC104 board. This is an old 386SL, with embedded RAM, flash "disk", Ethernet, three serial ports, a VGA/LCD display controller, printer ports, SCSI (!) port, etc. Neato, I've always wanted to tinker with a PC104 PC.
  • The LCD is an old NEC NL6448AC30-12, 640 x 480 with 12-bit RGB color (total of 4096 colors!) and a functioning backlight.
  • Attached to the LCD is some kind of capacitive MicroTouch touchscreen, with standalone controller. It's quite similar to this one from 3M (who bought MicroTouch), except without the light pen interface. It connects to the main board via RS-232 serial. Neato!
  • A nice, beefy +5, +12, -12, -5V switching supply.
  • Socketed Lucent OC12 modules, I guess? They have long fiber optic connections to the back panel.
  • A gross, decaying, leaking Lithium battery on the main board
  • A dead CR2032 on the PC104 (thankfully not leaking). No doubt any BIOS settings are long gone.

Mmmm, Vintage...


The newest ICs I have found on the boards date from very early 1997, so this thing is more than 20 years old. There are some nice throwback ICs on there that I remember from my ADC days, from the likes of Level One and TransSwitch.


Probing for Connections

The PC104 board plugs in to several connectors on the main board, from which it also derives power. After stripping it all down to gather information on the parts, I re-assembled it to see if it booted. It does! Kinda.

After the quickest possible flash of a POST success screen, I see an image like the one at the top of the page, which basically freezes with one square on the progress bar. Probably because two of the boards full of telecom peripherals aren't even attached anymore.

There is no obvious keyboard connection, so no chance to interrupt POST. But there are several connectors on the main board that were not connected to any of the telecom stuff. Checking out some hypotheses against the PC/II+ datasheet, I found that Digital Lightwave was very helpful, bringing out many of the unused features of the PC/II+ to handy connectors on the main board:
  • 34-pin FDD header, probably with the correct floppy pinout
  • 26-pin SCSI header, possibly with the correct pinout
  • 5-pin weird Molex connector for a keyboard. It even has the correct pin sequence for a PS/2 keyboard. I don't have the matching Molex connector, so I'll either hardwire an old PS/2 keyboard in, or something.
  • The PC/II+ COM2 is used for the MicroTouch controller
Additionally, some of the main PC/II+ features are right where I'd hoped:
  • The PC/II+ COM1 is wired directly to the main serial port on the back of the box
  • The PC/II+ Ethernet port is wired directly to the RJ45 on the back of the box

The LCD

I also probed out the fiddly LCD adapter cable. It is pretty simple, as it turns out. Oddly, the two LSBs of each of the RGB colors is tied together, so the display is really only uses 512 colors.

The backlight inverter seems to be dead simple, though I can't find a datasheet for it. It's powered by +12V from the supply, but there is one single conductor going all the way back to the main board, and a loop of wire connecting two of the inverter board pins together. I'm guessing the loop is some kind of safety interlock. The single conductor is held near 0V in normal operation, and when I chased down the trace on the inverter board, it went to a little SOT-23 part. I'm guessing that SOT-23 is a P-channel MOSFET, since the single conductor goes where I'd expect the gate pin to be, the usual drain pin is connected to the main chip's power pin, and the probable source pin is connected to +12V.

New Things I've Learned

One of many ICs on the main board is a Hitachi HD44238P. In hunting down a datasheet, I learned a bit about A-law and μ-law algorithms (though I confess I don't entirely understand the math behind them). Now that I think about it, it makes total sense to encode the quietest parts of audio with more bits than the louder parts, especially when you only have 8 bits to work with. The chip looks easy to work with, so I may desolder it and do some breadboard experiments.

End

That's as far as I've gotten reverse-engineering it so far. Once I get a keyboard hooked up, I'll see if I can get into the PC/II+ BIOS. Or see if it will boot from a floppy...