xcall CHKONE, c$
CHKONE is similar to TINKEY in that it allows you to check if a keyboard character is available, without getting stuck waiting if there is no character available. However, unlike TINKEY, which returns the actual character if available, CHKONE returns a "0" if no character is available, else "1". Any available characters remain in the input buffer, waiting for you to use another input routine to get them. c$ is a one-byte string.
