29 Mar
2012
29 Mar
'12
10:38 a.m.
On Mar 29, 2012, at 1:10 PM, Jon Elson wrote:
Well, I am chugging along on this project. After
fixing a few bugs,
I now have a program that will read single blocks off the tape.
Somewhere the docs got confused, they say that bit zero is MSB and
bit 7 is LSB, a la IBM 360. But, the data I am getting is clearly
the opposite bit order, so I will reverse that.
Good progress!
Also, I am not detecting file marks, but see a block
with zero
length. So, I need to look at that. Could easily be a wiring error.
Been a while since I've had to do a Pertec interface, so I can't
quite recall how those work.
But, I manually reversed the bits and I get VOL1 and
HDR1
records of 80 byte length, and then data records of 8192 length.
So, with just a little bit more tinkering, I think this thing is
going to work. It IS a nightmare, with a 44-pin TSOP memory
chip glued upside down on a piece of perfboard with wire wrap
wires soldered to it. It was the only suitable memory chip I
could find. 64K x 16, I'm only using one byte worth.
You know, if you're looking for a nice FPGA eval board which
provides 5v tolerant I/O and a decent amount of memory (SRAM,
SDRAM and flash), the Altera/Terasic DE1 is cheap and has 5v
tolerance (through clever use of the protection diodes and
current-limiting resistors). Its siblings may have the same
protection available, though I'm having some trouble finding
the schematics or anything mentioning it in the user manuals;
said siblings (DE0, DE0 Nano) use newer FPGAs, which might be
preferable.
- Dave