Unruh said the following on 05/29/2008 06:36 PM: > Since my GPS is only good to just under a usec, and since servicing of > interrupts is also at that level, it does not really seem to matter. The > program I wrote was to run off the parallel port interrupt, but it seems to > have about 2usec jitter on readout. > Ie for computer timing situations, a few nsec is overkill. How much cheaper > would a board with say 200ns output be? Is there a circuit diagram of that > kit anywhere?
The rise time of the MAX-232 chip is about 2.5us; there are some chips available that support 1 MBPS operation, and have much faster slew rates, but they violate the RS232 spec which requires a maximum slew rate of 30v/us (or about 330ns for +/-5v). The TADD-3 manual, which includes schematics, is at http://www.tapr.org/~n8ur/TADD-3_Manual.pdf On the TADD-3, there's essentially no added cost for the performance -- we just used 74AC chips which have the best performance of TTL logic chips. Of course, the input source needs to be quiet enough to make that performance usable. John _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
