QMS 1660 Reference Manual page 133

To differentiate data from the special control characters, any data that
is the same as one of the following special control characters must be
quoted.
ASCII ASCII
Keyboard Name
^A SOH
^C ETX
^D EOT
^E ENQ
^Q DC1
^S DC3
T DC4
FS
^\
A data byte is quoted by replacing it with a two-character sequence.
The first character is a ^A (ASCII hex 0x01), and the second charac-
ter is the character itself XORed with the ASCII value 0x40. For
example, to send the value 0x14(^T) as data, send the two-character
sequence 0x01 0x54 (^a T) instead. (ASCII "T" is the result of XORing
^T with 0x40).
This method of quoting guarantees that whenever the printer receives
any of the eight control characters, the control function is intended
regardless of whether the preceding character is a ^A. Any data byte
not equal to one of the eight special control characters is transmitted
by sending the data byte.
For more information on BCP and quoting, see the PostScript Lan-
guage Reference Manual (Adobe Systems, Inc., Reading, MA: Addi-
son-Wesley, 1990, ISBN 0-201-18127-4), the "Adobe Serial and
Parallel Communications Protocols Specification" (in Adobe Devel-
oper Support. Adobe Systems, Inc., February 14, 1992), and the
"PostScript Language Reference Manual" (in Supplement for Version
2011 , Adobe Systems, Inc., January 24, 1992).
ASCII Hex Control Function
0x01 Quote data character
0x03 Abort job and flush to end of file
0x04 End-of-file marker
0x05 (Reserved for future use)
0x11 XON in XON/XOFF flow control
0x13 XOFF in XON/XOFF flow control
0x14 Job status request
0x1C (Reserved for future use)