From: email@example.com (Mark Zenier)
Subject: Re: designing COM port interface without UART
Date: Sat, 26 Oct 2002 17:24:34 GMT
Organization: Eskimo North www.eskimo.com (800) 246-6874
NNTP-Posting-Date: 27 Oct 2002 17:03:02 GMT
In article ,
John B wrote:
>I'm reviewing the EIA-232 specification (formerly known as RS-232C). It
>describes hardware requirements, such as voltages, slew rates, etc. I have
>also read a basic primer on serial communiation, which says that EIA-232
>does not specify the type of pulse train used. That is, the asynchronous
>protocol is undefined by EIA-232. The same primer suggests two protocols
>for this purpose: "Two methods in which a data signal is self-timed are
>nonreturn-to-zero and biphase Manchester coding." I suppose there are
>I'm trying to build a DTE serial communication device that will communicate
>with the ordinary serial port of a computer or dumb terminal. (I realize
>I'll have to install a null-modem(i.e., criss-cross) in the cable, as
>computers and dumb terminals are themselves DTE devices.) A UART is not to
>be used. I would like to include RTS and CTS.
>I understand the pertinent standard to be EIA-232, but that alone doesn't
>tell me how to shape the asynchronous pulse train. Can anyone advise what
>protocol applies? If this is variable, what is the default?
If you're dorking around trying to figure out "Standardese" (the language
they write that stuff in), you might also have figured out that there will
be another standard that specifies the async. protocol.
As of the 1970's it seems to have been "Bit Sequencing of the American
National Standard Code for Information Interchange in Serial-by-Bit
Data Transmission", ANSI X3.15-1976. At least that's the one refered
to in my 1977 version of the ASCII standard. But that's bound to
be revised or superceded, probably by some ISO standard.
And probably ignored by half the industry anyway, especially if
Microsoft was involved.
Mark Zenier firstname.lastname@example.org Washington State resident