HP 1650B Programming Reference Manual page 308

Where <non-zero digif > is defined as a single ASCII encoded byte in the
range 31- 39 (49 - 57 decimal).
where c &bit byte > is defined as an &bit byte in the range 00 - FF (0 - 255
decimal).
Figure A-15. c arbitrary block program data >
c program data separator > . A comma separates multiple data
parameters of a command from one another.
Figure A-16. c program data separator >
HP 1650B/HP 16518
and
Message Communication System Functions
Programming Reference
A-16