
302 THE x86 MICROPROCESSORS
MOV AL, 90H ;control word
OUT CR, AL ;send it to the control register
IN AL,
PA ;take in data through Port A
CMP AL, 7FH ;compare it with 7FH
JA LOW ;if AL > 7FH,go to LOW
MOV AL, 0EH ;AL < 7FH,write a word for PC
7
= 0
OUT CR, AL ;send it to the control register
JMP XIT ;go to exit
LOW: MOV AL, 0FH ;AL > 7F,BSR word for PC
7
= 1 in AL
OUT CR, AL ;send it to the control register
XIT:
END ;end the program
us, we see that with the BSR mode, we are able to do ‘bit addressing’ for port pins, but only
for Port C, in the output mode alone.
9.5 | Mode 1
is is also called the handshaking mode. e features of this ...