24 Jul
2006
24 Jul
'06
10:01 a.m.
Dave Dunfield wrote:
The P4 comment implies that *all* PC's have this upper limit
(enforced in hardware? or, emulated in software??)
Does anyone
know what the available bandwidth of "standard"
parallel ports might be? E.g., on PC's I believe bus speed
is emulated at 8MHz (?) for I/O instructions (legacy). But,
what about other machines with parallel (printer) ports?
At one time I wrote a "PC logic analyzer", which monitors 13 input
lines from the parallel port (two reads per sample) in a tight assembly
loop to watch for a trigger condition, and then reads and buffers a
whole lot of samples at a user defined speed in an equally tight loop.
On most machines of 486 or better, the loop topped out at somewhere
around a 500khz sample rate. This is entirely bus speed limited - some
P4s do worse than some 486s. Thats a raw two-read tight loop with no handshaking -
once you put
some strobes and acknowleges in there, the actual throughput you
will realize will rapidly drop.