Re: EDD + CARD

[mjmahon@aol.com (Michael J. Mahon)]

Matthew Russotto replied:

>In article <20020731195944.08453.00001107@mb-mq.aol.com>,
>Michael J. Mahon <mjmahon@aol.com> wrote:
>>
>>With the bit stream at 250,000 bits per second, that seems unlikely.
>
>I thought so initially, but maybe not.  With external clocking, some
>serial ports might be able to handle that.

If the clocking is external, then the purpose of synchronizing to the
asynchronous "start bits" in the data stream is defeated.

If an external clock is used to put the USART into synchronous mode,
then Nyquist requires that the bit sampling rate be at least 500kbits/sec
to recover the data unambiguously, if the pulses were 50% duty cycle
(which they are not).

This would be easier to do with a serial-in/parallel-out shift register
interfaced to a parallel port.  Again, the shift clock would have to be
high to capture the pulses, but at 2MHz, the shift register would fill
in 4 microseconds, which is not too fast for a parallel port to read.

-michael

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