On Sun, 29 Dec 2002, John Lawson wrote:
> I did this once with ASCII paper tape: I made a loop that was triggered
> by the 'ready' bit and then sequentially tested each bit in the frame of
> 7, setting corresponding bits in a register, a kind of stupid software
> UART. The problem is to time the loop to be done right as the data bits
> are latched, and before the next 'ready' trigger...
The way I'm thinking to do it is to first determine what grouping the
character being read is in. It is either going to be in the 12, 11, or 0
"zone", or in the extended characters, the 8-3 zone. And then there are
the extended IBM character sets (i.e. EBCDIC) where you have 8-x zones
where x can be any number. What these represent is the 8 and x columns
being punched together as a sort of "meta" code (kinda like a control key
on a keyboard).
Then, there will be 1-9 possible characters in each zone. After
determining the zone, finding the correct character will be a matter of a
simple table lookup. The table will contain the ASCII character code of
that character, and then off that goes over the serial port to the
receiving machine (or buffered in some manner).
Doug Jone's article on punch card codes helped a lot. Doug Jones ROCKS!
> but the 6522 has hardware timers, no?
Jes.
> Once you've latched the card column data, you can store it in a
> super-frame that corresponds to the card itself - a 'column frame' and a
> 'unit record' frame.
I'll probably collect a whole card's worth of data before sending it out
the serial port. I'll have to see if this will be possible given the
speed of the reader (200 cards a minute). It should be possible to spit
it out in between card feeds at 9600bps:
80 characters x 11 bits = 880 bits / 9600 bps = .092 seconds. Should be
no problem. I'll see what the manual says about timing between card
reads.
...or I might be able to spit out characters as they are read, queueing
them in software if necessary. I think that's how I will go about it.
Sellam Ismail Vintage Computer Festival
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Received on Sun Dec 29 2002 - 11:08:00 GMT