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From: borg@inuxh.UUCP
Newsgroups: net.micro
Subject: Re: 1200 baud modem problems with break
Message-ID: <259@inuxh.UUCP>
Date: Fri, 20-Jan-84 08:58:16 EST
Article-I.D.: inuxh.259
Posted: Fri Jan 20 08:58:16 1984
Date-Received: Sat, 21-Jan-84 07:04:28 EST
References: <15373@sri-arpa.UUCP> <778@qubix.UUCP> <1201@mit-eddie.UUCP>
Organization: AT&T Consumer Products Div., Indianapolis
Lines: 17

Steve,
	The 212A standard is not frequency, but PHASE encoded.  I'm not
certain what the exact implementation of the 212A from what used to be the
Bell System is, but the received async data is buffered and reserialized
into SYNCHRONOUS bit stream.  I don't think the inability of a particular
212 implementation to transmit a break is filter related.  It's
most likely a problem in the digital circuitry used to deserialize the
incoming async data and generate the synchronous equivalent.
That is also the reason for the bit rate specs (1187 to 1212 baud?).
The clocks used for deserialization  must be set to something, and for
any clock value there is a limit to the range of speeds that will be correctly
received. (Try it on your own system.  Change the UART clock from the
normal value to something higher and lower.)  The 212A also does some
tricky stop bit deletion to enable it to handle terminals running at the
high end (1219 baud) of the operating range.  The receiving 212 then reassembles
a properly formatted character.