Tandy 600 Programmer's Reference Manual page 22

FUNCTION
OBh
-
Check
Keyboard
Status
AX
BX
CX
DX
SP:
BP:
SI:
Dl:
IP:
FLG
CS
DS
SS
ES
XXXXXXXX XXXXXXXX
Entry:
AH = OBh
(function
code)
Exit:
AL =
OOh
-
No
characters
waiting
FFh
-
Characters waiting
Function
OBh
checks
the
keyboard type-ahead
buffer
to
see
if
any characters are waiting
to
be
read.
It
will
return
AL
=
00
if
no
characters are
waiting, or
AL
= OFFh
if
any characters
are
waiting.
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