HLT and RUN LEDs

[Tom Lake]

Sometimes when a BASIC program is running the HLT LED is lit. If I raise HLT then lower it, the RUN LED comes on and HLT goes out. I can't pinpoint exactly when this happens but it's a fairly regular occurrence. I'd think that when the HLT LED is on, the processor would be halted. Is this what the original 680 did? 

[Chris Davis]

Can you tell me what BASIC program is running?  I have never seen this behavior.

[Tom Lake]

I found out how to repeat it. 

Turn on computer with power switch. 

Raise HLT and switch A0. HLT light is lit.

Press Deposit. BASIC load instructions are printed. HLT light is still lit.

Lower HLT and a dot prompt is printed. HLT light still lit.

Type J 0000   MEMORY SIZE prompt comes up. HLT is still lit.

Answer BASICs prompts. HLT light is still lit.

BASIC prints OK. 

You can now type in a program and run it or CLOAD from SD card and run. HLT light is still lit, RUN light is dark.

Raise then lower HLT. HLT light goes out, RUN light lights.

Even though you are running BASIC programs, the HLT light stays lit and RUN stays dark, at least on my system.

[Chris Davis]

I have four of them built here and I can't get this behavior on any of them.  I guess I'd check for continuity between D13 and D14 just to see if there's a short.  I'd also try swapping the U2 darlington array with another one and see if that has any effect.

[Tom Lake]

At which step below does the HLT light go out and the RUN light illuminate?

1. Turn on computer with power switch. 

2. Raise HLT and switch A0. HLT light is lit.

3. Press Deposit. BASIC load instructions are printed. HLT light is still lit.

4. Lower HLT and a dot prompt is printed. HLT light still lit.

5. Type J 0000   MEMORY SIZE prompt comes up. HLT is still lit.

6. Answer BASICs prompts. HLT light is still lit.

7. BASIC prints OK. 

[Chris Davis]

When the toggle is on RUN, the RUN LED is on, when the toggle is on HLT, the HLT LED is on.  The code that controls is it super simple.

The moment you lower the toggle, the LEDs should change, regardless of what else is going on.

[Chris Davis]

Does the RUN LED ever illuminate under any conditions?

[Tom Lake]

Perhaps it was a bit of dust or something in the HLT switch! I toggled it again and again and most of the time it switched the LEDs properly but occasionally it 
kept the HLT light lit and the RUN light off. I pushed in on it and toggled it a number of times and it hasn't missed since. I don't need to push in on it anymore, it just works.

On Tuesday, January 27, 2026 at 1:40:54 PM UTC-5 famousd...@gmail.com wrote:

[Chris Davis]

I had seen a couple instances where it appears the toggles had some oxidation build up while they were in storage.  

[George W4AVO]

My AD680 did the same thing  as Tom's. I small blast of CRC QD cleaner and a few cycles of HLT RUN fixed it.

Pix below shows the HLT LED on and the RUN LED off with the switch in RUN.