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would you program the computer so that the logic state at<br />
of the input port could be monitored Assume that there are<br />
ossible conditions:( a ) the other bits are grounded ( logic zero ) ,<br />
) the other bits may be used for other Hag inputs.<br />
e other bits are grounded, then the value from the input port<br />
e zero when the flag is cleared, and nonzero when it is set.<br />
other bits are used for flag inputs, then the "unwanted" bits<br />
'be masked. The masking operation uses the logical AND operaso<br />
an assembly-language subroutine would nave to be used.<br />
this case, you will enter the assembly-language program that<br />
d to perform the AND operation on two data bytes. Follow these<br />
to enter the program:<br />
Press the RESET key and type CALL -151 and press the RE<br />
TURN key. The Apple should respond with an asterisk ( 0 )<br />
when it is in the Monitor mode.<br />
Type 0300: 00 00 00 48 AD 00 03 2D 01 03 8D 02 03 68 60 Leave<br />
a space between the two-digit groups as shown. Use 00 for the<br />
first three values in the program.<br />
Press the RETURN key, type 02FF and press the RETURN<br />
key three times. Now, check the data shown on the display<br />
with the information that you entered.<br />
test this assembly-language routine, you may use the followprogram.<br />
Since the AND operation will use binary numbers, you<br />
have to convert your test numbers into binary so that you can<br />
k the results.<br />
POKE 10,76: POKE 11,03: POKE 12,03<br />
INPUT " MASK BYTE ";M: POKE 768,M<br />
0 INPUT " DATA BYTE ";D: POKE 769,D<br />
Q = USR(O): PRINT "ANSWER "; PEEK(770)<br />
0 GOTO 1010<br />
e program does not provide the proper results, re-enter the<br />
pitor mode and check the data bytes that you have entered.<br />
151
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