Jan 052014
 

The PPG Waveterm A was built around an industry processor board named EUROCOM II V7 made by ELTEC. Based on a 6809 CPU it contains two 6821 PIAs, a 6850 ACIA with baud rate generator, a 1793 FDC controller, 64k of dynamic RAM and two 4k ROM sockets. One out of three 16k memory pages can be mapped to the integrated discrete monochrom graphics controller.

Due to the complexity it can become rather complicated to trouble shoot those boards. As lots of counters and other TTL ICs are required for the memory to work properly, chances are good that an application’s firmware won’t run due to memory problems.

For the software I’ve created only the CPU, ACIA and baud rate generator need to work. The first routines run completely within the CPU registers and do not require any RAM.
Once started, a welcome message should appear on the connected terminal. If not, basic 6809 system troubleshooting needs to take place.

As soon as the terminal comes to live, the first 4k of RAM will be checked by a AA/55 pattern. If a mismatch occurs, the routine will stop and the original and read bit pattern is displayed.
Assuming the first memory page is in good condition, the stack pointer is initialized and a menu appears.

For now, four tasks are available:
1. Memory test. The whole memory between 1000 and EFFF will be tested, an error will be displayed with the actual address, the written and the read bit patterns. The test will run forever.
2. PIA output. All 8 bit PIA ports show a square wave with a frequency of 19.2kHz on PA0/PB0 decreasing to 150Hz on PA7/PB7.
3. PIA input. Binary patterns of all four 8 bit ports are displayed continuously.
4. Screen test. A test image will be show.

To Do’s:
– add two more test screens, switchable using the page select lines
– add a test for the hardware scrolling functions
– keep away from the FDC, this will have to be troubleshooted in the target system if necessary

ELTEC Eurocom II V7 board under test

A first impression of a Eurocom II on the emulator