thunter0512
Veteran Member
I have been using the SBC6120-RBC for a few years, but recently Chris Tersteeg has created a nice FP6120 front panel clone of Bob Armstrong's original. I have now noticed that there may be a problem with the SBC6120-RBC because the following little count program does not behave as expected on the SBC6120-RBC + FP6120, but works fine on Bob Armstrong's original:
0: 7001
1: 2101
2: 5001
3: 5000
On the original when you select the AC with the rotary switch, the LEDs continuously count from 0000 to 7777 forever.
On the RBC version the LED display freezes at about 7777 and then resumes what is approximately one full count cycle later.
When while in the frozen state I hit break on the console or toggle the Halt switch, I see that the program is running fine - just the LEDs are not updating.
In an effort to narrow down the culprit I have now replaced the SBC6120-RBC with Bob Armstrong's original SBC6120 and plugged that into Chris Tersteeg's FP6120 and it behaves correctly.
When I plug the SBC6120-RBC into Bob Armstrong's original FP6120 the data LEDs freeze as before. I also tried a second SBC6120-RBC and it too has the "freezing" behaviour.
This seems to indicate that there is some problem with the SBC6120-RBC as the problem follows the SBC6120-RBC.
When the display is frozen I see that the CPREQ signal keeps pulsing at approx 30 Hz.
The ROM Monitor in both SBC6120 (original) and SBC6120-RBC is version V320.
The original SBC6120 and both SBC6120-RBC run OS/8 without a glitch. There is no noticably freezing of the LEDs with OS/8 on any of the 3 SBC6120.
I wonder what could cause this:
Could some of you please try this if you have any FP6120 (original or Chris's version) and a SBC6120-RBC.
0: 7001
1: 2101
2: 5001
3: 5000
On the original when you select the AC with the rotary switch, the LEDs continuously count from 0000 to 7777 forever.
On the RBC version the LED display freezes at about 7777 and then resumes what is approximately one full count cycle later.
When while in the frozen state I hit break on the console or toggle the Halt switch, I see that the program is running fine - just the LEDs are not updating.
In an effort to narrow down the culprit I have now replaced the SBC6120-RBC with Bob Armstrong's original SBC6120 and plugged that into Chris Tersteeg's FP6120 and it behaves correctly.
When I plug the SBC6120-RBC into Bob Armstrong's original FP6120 the data LEDs freeze as before. I also tried a second SBC6120-RBC and it too has the "freezing" behaviour.
This seems to indicate that there is some problem with the SBC6120-RBC as the problem follows the SBC6120-RBC.
When the display is frozen I see that the CPREQ signal keeps pulsing at approx 30 Hz.
The ROM Monitor in both SBC6120 (original) and SBC6120-RBC is version V320.
The original SBC6120 and both SBC6120-RBC run OS/8 without a glitch. There is no noticably freezing of the LEDs with OS/8 on any of the 3 SBC6120.
I wonder what could cause this:
- The SBC6120-RBC is a double layer board whereas the original is a 4 layer board. Possibly when AC wraps from 7777 to 0000 it causes some noise on the 2 layer board which disturbs something.
- The PAL firmware may be subtly different.
Could some of you please try this if you have any FP6120 (original or Chris's version) and a SBC6120-RBC.