User`s manual

Operation Theory 27
72XX Series
User’s Manual
4.1.5 Control Word
The control word written in the control port is used to setup PA,
PB, and PC as input or output port. Figure 4.1 shows the format of
the control word. Table 4.2 shows the 16 possible control words
and the respective I/O configurations.
Figure 4-1: Control Word Format
Table 4-2: Summary of control word (D0-D4)
Note: * Power on default configuration.
Control
Word
D4 D3 D1 D0 PORTA PORT C UPPER PORT B PORT C LOWER
00H 0000 O/P O/P O/P O/P
01H 0001 O/P O/P O/P I/P
02H 0010 O/P O/P I/P O/P
03H 0011 O/P O/P I/P I/P
08H 0100 O/P I/P O/P O/P
09H 0101 O/P I/P O/P I/P
0AH 0110 O/P I/P I/P O/P
0BH 0111 O/P I/P I/P I/P
10H 1000 I/P O/P O/P O/P
11H 1001 I/P O/P O/P I/P
12H 1010 I/P O/P I/P O/P
13H 1011 I/P O/P I/P I/P
18H 1100 I/P I/P O/P O/P
19H 1101 I/P I/P O/P I/P
1AH 1110 I/P I/P I/P O/P
1BH* 1111 I/P I/P I/P I/P
X
X X
?
?
?
X
?
1/0 : Input/Output of Port C low nibble
D7 D6 D5 D4 D3 D2 D1 D0
1/0 : Input/Output of Port B
1/0 : Input/Output of Port C high nibble
1/0 : Input/Output of Port A
X : don't care