Radio Shack TRS-80 Model II Reference Manual page 193

Technical Information
KBINIT
Keyboard Initialize (function code 1)
This routine initializes the keyboard input driver. This call should be made
before you start keyboard input. It clears all previous keystrokes.
Entry Conditions
A= 1
Exit Conditions
NZ=
A=
Error
Error Code
KBCIIAR
Keyboard Character (function code 4)
This routine gets one character from the keyboard. The routine returns
immediately either with or without a character in register B.
The key is masked from the user - it will never be returned, since it
is intercepted by the System. If aSETBRK routine is enabled, control passes to
the processing program (see SETBRK) whenever is pressed.
Otherwise, control pass to TRSDOS READY.
Entry Conditions
A= 4
Exit Conditions
B
=
Character found, if any. Only codes within the range [0,127J can be
returned. If no character is returned, B is unchanged.
NZ
=
No character present
A
=
Error Code
229