Tandy 1000 HX Technical Reference Manual page 393

Keyboard
16 hex (22 dec)
Function Summary:
AH = 0: Read Keyboard (destructive with wait)
AH = 1: Scan Keyboard (nondestructive, no wait)
AH = 2: Get Current Shift Status
Function Descriptions:
Read Keyboard
Read the next character typed at the keyboard. Return the
ASCII value of the character and the keyboard scan code, remov-
ing the entry from the keyboard buffer (destructive read).
Entry Conditions:
AH = 0
Exit Conditions:
AL = ASCII value of character
AH = keyboard scan code
Scan Keyboard
Set up the zero flag (Z flag) to indicate whether a character is
available to be read from the keyboard or not. If a character is
available, return the ASCII value of the character and the key-
board scan code. The entry remains in the keyboard buffer (non-
destructive read).
Entry Conditions:
AH = 1
Exit Conditions:
Z = no character is available
NZ = a character is available, in which case:
AL = ASCII value of character
AH = keyboard scan code