Briel Computers support forum

"Welcome to Macintosh (film)" was on Wikipedia's "Did you know..." section of their front page today. The article lists the stars including Andy Hertzfeld .. and Vince Briel!

and it's available on Netflix.

So what's it like to be a movie star?

Vince, Oh my god. The superboard was the first computer I ever owned! I bought it in the late '70s for I think it was $250. That's all I could afford at the time. It was the cheapest computer I could find that could actually do something without investing in a teletype or dumb terminal. Later I boug...

Oops.
I see from the datasheet that the 8085 has a maximum clock period of 2000nS. So you can't just stop the clock. You have to use the READY line.

If you try to control the microprocessor using the READY line, the timing's pretty tight. The ALE line is high at the begining of each machine cycle. Then you have only about one clock cycle to drop the READY line. You would have to have a pretty fast microcontroller to detect the ALE change and dro...

I'm quoting the data sheet when I say it's 100% software compatible. From what I've read, the only issue between 8080 and Z80 software compatibility is the Parity/Overflow bit, and it seems that the 8085 behaves the same as the 8080. Obviously there are hardware differences. The number of cycles per...

Apparently the Z80 redefines the Parity status bit as Overflow for math operations. There is a disassembly of 4K basic here: http://www.interact-sw.co.uk/altair/index2.html It looks like in the printing floating point number to the terminal routine, it uses JPO (Jump Parity Odd) in part of a loop. P...

Most of the old minicomputer front panels had access to the accumulators or registers from the front panel. That would be quite a trick for a microprocessor based system. There's a challenge for you to think about. How to single step, display and or modify any register from the front panel, and cont...

Hi Vince, The Altair 8800 theory of operations manual pretty clearly explains how the front panel works. As you said, for the Examine switch, it jams a JMP instruction onto the DATA bus, followed by the 2 address bytes set on the switches. When the 8080 executes the jump, the 8080 asserts the addres...