By Aaron Priven
This is a little text file for all of the novices out there like myself
who have wandered in on the world of computing eager for knowledge but who have found very little. This is a table of the ASCII codes. "What? you ask? The ASCII codes? Why that's easy. 32 is space, and 33 is the exclamation point, and 34 is the double quote…" All true, except that the code starts at 0. Well, I imagine that all of you have heard of "NUL"s or null characters, and probably "NAK"s (which are used in Xmodem Checksum protocol) but what are the other mysterious codes between 0 and 32?
Well, friends, this is your opportunity to find out. Because I am going to tell you. Now don't get the idea that I have been in the computer business since 1956 and was on the committee that invented the ASCII codes. I wasn't born till 15 years after that and I got interested in computers two years ago. I simply stumbled on this very interesting table in the VisiFile manual (a very bad program marketed by the late lamented VisiCorp that came with my computer) that not only included the number and two- or three-letter mnemonic (a fancy "computerish" word for name) but what the codes were actually intended to do! (Yes, it sounds too good to be true.) So I decided to gift you all with this table.
Oh, if you think this is stealing their manual material, for one thing
the ASCII codes are far from copyrighted. And VisiCorp is but a small part of data in the computer-industry's (read-only?) memory.
And heeeeeeeere's Tabley:
CODE NUMBER MNEMONIC WHAT THE HECK IT DOES
00 NUL Null character (nothing) 01 SOH Start heading 02 STX Start of text 03 ETX End of text 04 EOT End transmission 05 ENQ Enquiry 06 ACK Acknowledge (We heard you and yes.) See NAK 07 BEL Bell (BEEEEEEP!) 08 BS Backspace 09 HT Horizontal tab 10 LF Line feed 11 VT Vertical tab 12 FF Form feed (clear screen) 13 CR Carriage return (enter) 14 SO Shift-out 15 SI Shift-in 16 DLE Data link escape (I don't know what this is either) 17 DC1 Device control #1(maybe they ran out of things to do?) 18 DC2 Device control #2 19 DC3 Device control #3 20 DC4 Device control #4 21 NAK Negative acknowledge (We heard you, but no.) See ACK 22 SYN Synchronous idle (let's sit around doing nothing) 23 ETB End transmission blocks (whatever that means) 24 CAN Cancel (Whoa, Nellie!) 25 EM End medium (kill that conjurer!) 26 SS Special sequence 27 ESC Escape 28 FS File separator 29 GS Group separator 30 RS Record separator 31 US Unit separator 32-126 – Normal characters – 127 DEL Delete
The parts in parentheses are my own little comments, or explanations.
I still don't know what some of them (the codes) mean. The other thing one must remember is that these were originally for teletypes and not computers, so that way "Synchronous idle" and the "Acknowledge" family make more sense. SYN means that someone doesn't want to do anything just yet. ACK and NAK are in response to a question. ACK means "Yes, we heard you, and the answer is yes." NAK means "Yes, we heard you, but the answer is no." Presumably if the questioner recieves anything else then the questioner means "What?"
Other ones that make sense to me but might not to other people: ENQ was
more than likely the thing people sent when they wanted an ACK or NAK. BEL is a bell because electronic speakers on teletypes were not common. VT probably meant "Go to the next vertical tab row" just as a normal tab means "Go to the next tab column." FF means to go to the next page; because there are no pages on a video screen it is interpreted to mean "Clear the screen." I'm not sure what SI and SO are supposed to do. I doubt if people would have bothered with other typefaces or compressed type on the old teletypes. DCx probably means they had four characters to fill so they put in something meaningless like "Device controls." "End medium" is a complete mystery to me. SS is of course for codes relating to things they hadn't thought of at the ASCII committee. FS,RS,US,and GS I should think would be for a database, but they didn't put databases on teletypes did they? And why they made DEL all the way back in the end when they could have just eliminated DC4 or something is beyond me.
If you like this text file, please send 10 cents to the above address.
Aaron Priven 540 Sylvan Avenue San Mateo, CA 94403-3214 U.S.A.
Foriegn currency accepted! e address.