Thanks, Jason. Interestingly, it's really hard to find a clear answer to the definition of "assert" and "clear" on the web.
One reference I'm looking at now says: " A low level (–3 to –15 volts) is defined as a logic 1. asserting a logic 1 or turning on a signal is historically referred to as “marking”. A high level (+3 to +15 volts) is defined as a logic 0. Releaseing to logic 0 or turning off the signal is referred to as “spacing”. " (http://www.piclist.com/techref/io/serial/rs232sigs.htm). That would indicate that "assert" is going positive-to-negative voltage or going from logic 0 to logic 1. By implication "clear" would be the opposite, or a negative-to-positive transition. That would indicate the opposite of what you said. But another reference, http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html, says " Pin 8 - Received Line Signal Detector (CD) (also called carrier detect) This signal is relevant when the DCE device is a modem. It is asserted (logic '0', positive voltage) by the modem when the telephone line is "off-hook", a connection has been established, and an answer tone is being received from the remote modem. The signal is deasserted when no answer tone is being received, or when the answer tone is of inadequate quality to meet the local modem's requirements (perhaps due to a noisy channel). " More generally, that reference consistently uses "assert" to mean a positive voltage, logic 0. But it doesn't use the term "clear" in that context but says "deasserted". I can't vouch for how definitive this reference is, but it seems to be thorough and internally consistent, so I tend to believe it. Based on that definition, your statement is correct. It also seems clear that there's plenty of room to get very confused about all this. We really need to document this. When I get the strength, I'll try to add something to the wiki. Thanks! John ---- [EMAIL PROTECTED] said the following on 10/15/2006 12:34 PM: > John, > > In RS-232 terms: > > Assert = Positive Voltage = logic 0 > Clear = Negative Voltage = logic 1 > > The only reason I mention the logic 0 & 1 is because in TTL terms it's > backwards. A logic 0 for a TTL signal is 0 volts, and a logic 1 is ~5 > volts. Many GPS devices that have a PPS output at TTL voltage levels (0 > - 5v) but are RS232 biased. So if you tried to stick like a MAX232 chip > on there to bring the voltages into the full RS232 voltage levels it > would end up being upside down. You would need a voltage inverter to > flip it back. It's best just to leave it as-is if the GPS device says > they are already RS-232 biased. > > Back to your question though... > > flag2 0 = Voltage goes from low to high at the timemark (default) > flag2 1 = Voltage goes from high to low at the timemark > > _______________________________________________ > questions mailing list > [email protected] > https://lists.ntp.isc.org/mailman/listinfo/questions > > _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
