Technical Notes

By: Widgets And Gadgets  05-Apr-2012

Notes on ASCII Communication over a RS232 communication link.

RS232 (Recommended Standard 232) is an EIA standard for the three wire full duplex  electronic communication protocol, introduced in 1962. It has gained industrial acceptance and wide spread use.

ASCII (American Standard Code for Information Interchange) is the data type traditionally transmitted over a RS232 communication link. The standard was introduced in 1963.  RS232 files includes control characters to assist with formatting the received document.

RS232 and ASCII were developed to facilitate communication between machines and to to efficiently and correctly transfer documents over great distances.

As telecommunications has evolved from telegraph and Morse code through to personal hand held post offices both RS232 and ASCII have morphed into knew forms, for example USB, and UNICODE’s.

A nice feature of the ASCII text file format is that control codes are appropriately embedded within the formatted binary file allowing the message to be authentically reproduced over long distance.

To allow for the transmission of files that are not text based, such as picture information, a binary feature is provided that will treat all characters as non control codes.  An  example of the effect of the Binary feature on a control code is shown here, using a line feed character” $0A” as an example

From the ASCII table the Line Feed control character = $OA

While the ASCII Binary equivalent, in hexidecimal = $30, $41.

Where $ denotes that the data is in hexidecimal (hex) format.

Hex OA = ASCII hex 30 (O) followed by hex 41(A).

The ASCII bytes are transmitted in reverse order over a RS232 communications link, ie 41, 30

The information in this article was current at 27 Mar 2012

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