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  Constant:  _KEYBRD_READ, _KEYBRD_READY, _KEYBRD_SHIFTSTATUS,
             _NKEYBRD_READ, _NKEYBRD_READY, _NKEYBRD_SHIFTSTATUS
 
  Include:   <bios.h>
 
  Context:   _bios_keybrd
 
  Synopsis:  The <service> argument can be any one of the following
             manifest constants:
 
     Constant                 Meaning
 
     _KEYBRD_READ,            Reads the next character read from the
     _NKEYBRD_READ            keyboard. The _NKEYBRD_READ constant is
                              used with enhanced keyboards to obtain
                              the scan codes for function keys F11 and
                              F12 and the cursor control keys. If no
                              character has been typed, the call will
                              wait for one. If the low-order byte of
                              the return value is nonzero, it contains
                              the ASCII value of the character typed.
                              The high-order byte contains the keyboard
                              scan code for the character. See ◄SCAN.H►
                              for a list of keyboard scan codes.
 
     _KEYBRD_READY,           Checks to see whether a keystroke is
     _NKEYBRD_READY           waiting to be read and, if so, reads it.
                              The _NKEYBRD_READY constant is for use
                              with enhanced keyboards. The return value
                              is 0 if no keystroke is waiting;
                              otherwise, the return value is the
                              character waiting to be read, in the same
                              format as the _KEYBRD_READ or
                              _NKEYBRD_READ return. This service does
                              not remove the waiting character from the
                              input buffer, as does the _KEYBRD_READ or
                              _NKEYBRD_READ service.
 
     _KEYBRD_SHIFTSTATUS,     Returns the current shift-key (SHIFT)
     _NKEYBRD_SHIFTSTATUS     status. The _KEYBRD_SHIFTSTATUS uses only
                              the low-order byte of the return value.
                              See ◄SHIFT.H► for a list of keyboard
                              shift codes.
 
     Any combination of the following status bits can be set:
 
     Bit                      Meaning
 
     00H                      Right SHIFT key pressed
     01H                      Left SHIFT key pressed
     02H                      Either CTRL key pressed
     03H                      Either ALT key pressed
     04H                      SCROLL LOCK on
     05H                      NUM LOCK on
     06H                      CAPS LOCK on
     07H                      In insert mode (INS)
     08H                      Left CTRL key pressed
     09H                      Left ALT key pressed
     0AH                      Right CTRL key pressed
     0BH                      Right ALT key pressed
     0CH                      SCROLL LOCK key pressed
     0DH                      NUM LOCK key pressed
     0EH                      CAPS LOCK key pressed
     0FH                      SYS REQ key pressed