Matthew Smith wrote: > Quoth Hal Murray at 2008-03-06 20:07... > >>> I will be doing (4) as soon as I've found the time to make up a TTL to >>> RS232 board. >>> >> I suggest trying it without anything fancy. >> >> All the GPS toys I've tried work fine without any conversion gear. >> >> The normal TTL to RS-232 chips include an inverter. That will break things >> unless you add another inverter. (or your gear expects an inverter) >> >> The usual switching point for RS232 receiver chips is 1.4 volts. That's the >> switching point for TTL inputs, 2 diode drops above ground. That works fine >> for 3V CMOS drivers. >> >> >> > > So my Trimble ACE II and Moto Oncore modules will tolerate RS232 levels > without conversion? Are we absolutely sure on this - I don't want to > fry anything! > > Cheers > > M > > Matthew
All that has been stated is that the receiver modules wont be damaged when driving an RS232 input. However when an RS232 input drives a 3V CMOS input there are no guarantees. In the latter case a series resistor at the CMOS input can be used to guarantee the COS gate isnt destroyed. In general it would be better to use a CMOS - RS232 converter chip, it can be socketed and used as a fuse (considerable cheaper than using the GPS receiver outputs as a fuse) should anything untoward occur. Also CMOS devices arent rated to continuously drive a short circuit a series resistor to limit potential fault currents to the datasheet maximum is advisable. 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.
