Early Microprocessors in Industrial Microcomputers

Jon Elson elson at pico-systems.com
Wed Mar 9 23:45:59 CST 2016

On 03/09/2016 08:43 PM, Chuck Guzis wrote:
> On 03/09/2016 08:49 AM, Jon Elson wrote:
>> The row of red LEDs at the bottom of the pic is the front 
>> panel of
>> the 7300 CPU.  They had an industrial control bus that 
>> allowed you to
>>  connect a wide variety of interface boards, like encoder 
>> counters,
>> DACs, digital inputs and outputs, etc.  It used 
>> battery-backed DRAM,
>> and was made around 1978.
> Much of the old Mitsubishi CNC gear uses battery-backed 
> RAM via a lead-acid storage battery "floated" on a 
> supply.  A tape or diskette drive is used for loading it 
> with parameters and software.  Once read, the floppy isn't 
> used for regular operation.
The A-B was loaded from paper tape.  I didn't get the CNC 
executive with it, just the CPU diagnostics.
I found a guy on the net who serviced these oldsters and 
made a tape on one of his customer's machines.
I then had to write a disassembler and patch the code to 
make it work on my specific setup.  Mostly, I had to change 
the encoder resolution.  Lucky for me, it was only a 2:1 
change.  I quickly built a "BTR"  (behind the reader) 
interface to a laptop, and used it to download the executive 
and then it drip-fed the CNC program a line at a time to the 
A-B control.

When CPU power was off, the DRAM arrays were powered up 640 
times a second and a complete refresh cycle was done, then 
the DRAMS were powered off again.  If you leaned close to 
the memory power supply, you could hear the 640 Hz tone.


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