Register parameters
RST 20H, DEFB $30
IN: -
OUT, if call successful:
Fc = 0, input MAY BE available
A = input source
XIN_KB ($01), keyboard buffer has data, possibly ESC or pre-emption
XIN_RX ($02), serial RX buffer has data
XIN_CLI ($04), CLI is active
OUT, if call failed:
Fc = 1
A = error code:
RC_EOF ($09), OS_In will not return immediately if called
RC_HAND ($08), bad handle
Registers changed after return:
..BCDEHL/IXIY same
AF....../.... different
Notes
The function of this call is not so much to tell you when input is available, but rather to indicate when it definitely is not.
The call might be useful to examine if OS_In is going to return a pre-emption error like RC_SUSP or RC_QUIT. Possible reasons are:
pending character
exception code (e.g. RC_SUSP due to machine reviving)
input available
Related calls
GN_Sip, system input line routine
OS_In, read (wait for) character from standard input
OS_Pur, purge keyboard buffer
OS_Tin, read character from standard input, with timeout