Radio Shack TRS-80 Model II Reference Manual page 209

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Technical Information
PRCHAR
Print Character (function code 18)
This routine sends one character to the Printer.
Note: Most printers do not print until their buffer is filled or a carriage
return is received.
Entry Conditions
B
=
ASCII
code for character to send
A
=
18
Exit Conditions
NZ
=
Error
A
=
Error Code
Notes
While the serial printer option is selected, allowing printer output to Channel B,
two
INPUT
characters are recognized from Channel B. These will affect all serial
printer output operations:
ASCII
Name
DC3, "CTRL-S"
DC I , "CTRL-Q"
Hex
Code Result
13 Pause printing
I I Resume printing
Certain codes are normally intercepted by
TRSDOS
and are not sent directly to the
printer. There are several ways to override some or all of these character
translations. See
SVC PRINIT
and
SVC PRCTRL.
Table of Intercepted Codes
ASCII
Hex
Name Code
Tab 09
Vertical OB
Tab
Form
OC
Feed
Carriage
00
Return
Special
Result to Printer
From one to eight spaces are sent to provide a tab function.
Same as form feed below.
TRSDOS
sends enough carriage returns or line feeds to the printer
to advance the paper to the next top ofform.
When the current line is empty (no characters printed since the
last carriage return or line feed), this is translated as a line feed to
allow correct operation of Radio Shack printers. In the auto line
feed mode,
X'OA'
is sent after every
X'OD'.
80
TRSDOS
sends a carriage return to the printer. In the auto line feed
mode, using this code allows you to send a carriage return
without a line feed.
245