TI-H: Parallel Port Expander

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TI-H: Parallel Port Expander

Today I finally got my Parallel Port Expander to work correctly and I 
think consistently.  Basically, all it does it receive 8 clocked bits 
from teh link port and output them in parallel format.  I'm not going 
to post the schematics yet because I have yet to come up with a way 
to synchronize the circuit with the calculator without having to turn 
off and on the circuit.  But it does work, at at very high speeds.  
In normal mode, it transfers 4096 bytes from ROM in a little over 2 
seconds, and in turbo mode, about 1 second.  These transfer to about 
16 Kbps (bits per second) and 32 Kbps, respectively.  This is pretty 
close to the maximum transfer rate for the link port, because I don't 
think the software can be optimized much more.  But, still this is a 
very high transer rate.  With the Serial Flash Expander transfering 
at these speeds, it could copy 28K in either 14 or 7 seconds, 
depending on the mode and also depending on how fast the software is 
and how many address bytes it has to send.  But, for those of you 
interested in video playback, this would be either 2 or 4 frames per 
second, which is pretty good for a calculator.


-Ed