Bruce and Luis, > Using a 74HC244 may be somewhat problematic with CPLDs that > don't have 5V tolerant inputs. Even when using a device with > 5V tolerant inputs a 74HCT244 may be more suitable for > translating LVCMOS logic level outputs from the CPLD.
One chip that works very well for TDI/TMS/TCK translation from the printer port into the cpld is the 74AHC125 with its VCC connected to the cpld's VCC. This one can work with VCC as low as 2.0 V and is still 5 V tolerant on all inputs. At least with 3.3 cplds it's output swing is high enough for TDO back-translation. With 2.5 / 1.8 V cplds a separate TDO back-translation may become necessary. Best regards Ulrich > -----Ursprungliche Nachricht----- > Von: [email protected] > [mailto:[email protected]] Im Auftrag von Bruce Griffiths > Gesendet: Donnerstag, 2. April 2009 23:38 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] Frequency Divider > > > Luis Cupido wrote: > > > > > >> The CPLDs are programmed via the JTAG port. > >> Suitable JTAG programming cables are readily availble. > >> > > > > Or you can build one to use the LPT port of your PC using just a > > 74HC244. > > > > > > Luis Cupido. > > ct1dmk. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > Luis > > Using a 74HC244 may be somewhat problematic with CPLDs that > don't have 5V tolerant inputs. Even when using a device with > 5V tolerant inputs a 74HCT244 may be more suitable for > translating LVCMOS logic level outputs from the CPLD. > > Bruce > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
