A peek inside an ISDN terminal

80C32 microprocessor and firmware EPROM

If you get the chance to grab an electronic device headed to the recycle factory, don't you want to tear it apart?

I got a desktop telephone that turned out to be an ISDN terminal. That's not my field of expertise, but I know it won't work if I plug it in the normal PSTN landline.

I took it home for the LCD display, but things got interesting!

The first glance inside reveals that the device is actually an 8-bit microcomputer, with an 80C32 processor and a 256 kbit UV-EPROM which probably contains the firmware. With a lot of time to spare, a new firmware could be written to turn the thing into an unconventional self-contained microcomputer: it has 40+ keys and a 20x4 character display after all! The device was built around 1996 and the LCD display already spoke the now well-known HD44780 protocol!

And even if you would just unsolder components, there are quality capacitors and machined-pin sockets beyond the microprocessor, LCD, EEPROM, 32 ohm speaker.

The circuit board of this ISDN terminal.

If I could only manage to power it up...

Keyboard, HD44780 display, speaker.

And I just remembered I have an advanced PSTN telephone in the junk pile. Must look into it too!