[TI-H] Parallel link woes, how does screenshot work etc.
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[TI-H] Parallel link woes, how does screenshot work etc.
Hi all!
This is my first post to this mailing list, and it will be pretty long, try
to bear with me! :)
I have tried to build a parallel link cable to use with my TI-83, but
I can't get it to work. I've tried it on 7 or 8 different computers, I have
installed an old ISA controller card, I've tried it with another calculator
(both worked find when linked to eachother) and I've checked the cable with
a multimeter to see that all connections are OK.
All programs that feature a test segment (linktest, Cal) report that the
cable is working just fine. But when nothing worked I wrote a simple program
that monitored the parallel-port status, and it seemed like the signals that
the calculator sent never came through, the value returned from port 378h
returned 3 all the time. When using a link-program set to 'send' mode it
changed to 1 or 2, but it seemed like the calculator never responded to
this. I then decided to do some tests with a multimeter:
* Cable not connected to the computer:
- Pins 2 and 3 (also 12,13) are at 4-5V when the calculator is in 'normal'
mode.
- Pins 2 and 3 (also 12,13) are at about 0V when the calculator is set to
send a file.
This seems to be the way it should.
* Cable connected to LPT1 (but no link software running)
- Pins 2 and 3 at 3.3V (12,13 somewhat higher) when the calculator is in
'normal' mode.
- Pins 2 and 3 still at 3.3V when the calculator is set to send a file, but
12 and 13
go down to about 1V.
Shouldn't 2 and 3 also go down to 'low' level at this point??
Isn't pin 2 and 3 those that the computer uses to read input from the calc?
Since they don't change to anyhting but 3.3 even when the calc tries to send
a low (0) signal, this seems to be why my calc isn't working. The quesion
though is WHY is this happening?
Then I read in Andreas Westfeld's FAQ that pins 2,3 are used for _sending_
only, and that 12,13 are used to read. In that case, the problem I described
above is not a problem, since 2,3 shouldn't change when the calc is sending
then. But if this is the case, isn't the diodes switched wrong then? I mean,
the data you set at 2,3 can't make it's way onto the cable! If 2,3 are meant
to READ data from and 12,13 meant to send, it would make more sense. Or am I
misinformed?
Anyone can give an in-depth explanation on how exactly the communication
parallel-port <-> calculator port is supposed to work (which bits are set at
which pins etc.)
Or maybe I should try to build the serial link instead? Does it have a
higher 'success' rate?
Finally, can someone explain how screenshot-functions in transfer programs
are supposed to work? I mean, the calc is not supposed to be in send mode,
how does it know that it should start sending a screenshot? Does it
constantly poll the link-port when in 'normal' operating mode?
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