Post by thread:Caller ID (was Re: LED matrix multiplexing (Correc

You wrote: >Here in North America, caller ID information is sent as standard 1200 baud >ASCII text between the first and second ring. The signals are exactly like >the ones used by your 1200 baud modem. My modem uses the "full duplex" version of Bell's 1200 baud protocol. My understanding was that Caller ID used the prior "half duplex" protocol (sender gets full band rather than half band). I forgot the protocol's name. Yes, I know that would be helpful. -- Hank

> You wrote: > > >Here in North America, caller ID information is sent as standard 1200 baud > >ASCII text between the first and second ring. The signals are exactly like > >the ones used by your 1200 baud modem. > > My modem uses the "full duplex" version of Bell's 1200 baud protocol. My > understanding was that Caller ID used the prior "half duplex" protocol > (sender gets full band rather than half band). I forgot the protocol's > name. Yes, I know that would be helpful. > > -- Hank What most people think about when they hear "1200 bps modem" is a Bell 212 compatible modem. This is a full-duplex modem, and actually a 600 baud PSK modem, with two bits encoded per symbol. The modems used for callid are the (even older) Bell 202 compatible modem, and they are half duplex plain FSK modems, much like the older Bell 103 300 bps modem. These are 1200 bps with (I believe) a low speed back channel. For caller id applications (and also, strangely enough, Amateur Packet Radio), it's the 1200 bps FSK modem you need to implement. Louis Mamakos