Anthony Whitehead, of Seeburger, Inc., wrote on Wednesday: "I have a
customer who received a sub-element separator of hex 14 (ASCII code is
DC4 and the EBCDIC code is RES) in layman's terms what is this
separator?"
Dear Anthony:
See the History of ASCII, the American Standard Code for Information
Interchange, by Tom Jennings, at http://www.wps.com/texts/codes/, where
he explains the purpose of the ASCII control characters (those whose hex
value is 00 through 1F). He describes DC4 (or Device Control 4) as a
"secondary control for auxilliary equipment; similar to DC3, but instead
to modify the behavior of the auxilliary device, such as pause,
interrupt, etc(2). Little used." I think DC4 had to do with something
called "paper tape," which I know nothing about because I am youthful,
self-absorbed, baby-faced and think History began with me.
Hex 14 is indeed the EBCDIC RES (Restore) control code, but since DC4
exists in both character sets, any transparent translation between ASCII
and EBCDIC should preserve the DC4 control character; DC4 is hex 3C in
EBCDIC.
More importantly, when considering EDI, is to avoid using control
characters either as data or separators because there may be a
possibility of them being interpreted as communications control (and
hence being dropped, mistranslated, or interrupting the transmission) .
Both ANSI ASC X12.5 - Interchange Control Structures - and ISO 9735 -
the EDIFACT syntax - warn that communication control characters may have
an effect on a transmission system, or might not be translatable or
supported on various platforms - i.e., they should be used with caution.
These characters are not a problem in modern TCP/IP Internet
communications, but would be something to think of when using old stuff
like Kermit, asynch protocols, or maybe even bi-synch 3780.
I doubt there was anything more significant in the sender's choice of
DC4 as a separator other than to avoid use of a printable character
(like colon - which may be used as a data character in element values)
and to ensure transparent translation between EBCDIC and ASCII.
William J. Kammerer
FORESIGHT Corp.
4950 Blazer Memorial Pkwy.
Dublin, OH USA 43017-3305
(614) 791-1600
Visit FORESIGHT Corp. at http://www.foresightcorp.com/
"Commerce for a New World"
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