HP 7970E - interest to split?

Jon Elson elson at pico-systems.com
Fri Sep 29 11:33:00 CDT 2017

On 09/29/2017 10:56 AM, Henk Gooijen via cctalk wrote:
> On a related note my plan is to make a USB-based, Pertec-compatible
> controller for it. Not sure how SimH connects with peripherals so I'm
> /very/ eager to talk with someone familiar with its workings. I'll also
> release all the board files and firmware as open-source. Timeline as always
> is completely unknown, though I do have a now-vested interest in making it
> work.
MANY, MANY years ago I got a surplus Pertec key to tape 
system that had a 7" 9-track 800 BPI NRZI drive connected to 
hardwired logic. You could key in data, verify data by 
re-keying it, and read back data to a panel of light bulbs.  
It had core memory for the data buffer.

I found the right place to slice the sections apart and have 
what was pretty close to the unformatted Pertec interface.
I then wrote a mostly software-driven interface to read and 
write tape blocks on my CP/M Z-80 system.  I created tapes 
and took them in to work to map them and got it to write 
ASCII text files in VAX ANSI-D format.  It really was not 
that complicated.  This was a read/write drive with only a 
single data gap.  So, to write and check a record, you had 
to write it, back up and read it.  I used it for making backups.

I think you could use a Beagle Bone and the PRU 
microcontrollers in it to do a Pertec unformatted interface.
The only issue is that the PRUs have a fast local memory of 
very limited size.  There is a way to open a memory
map to the ARM system memory from the PRU, although the 
shared memory is 12 K bytes, which might be enough to handle 
many uses.

I did an FPGA-based adapter to Pertec formatted interface 
using the parallel port.  (Slow, but I already had all the 
FPGA and computer side infrastructure to make that work.)  I 
have some CDC Keystone (92185) drives.


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