11
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
3827 Group
I/O PORTS
Direction Registers
The I/O ports have direction registers which determine the input/
output direction of each individual pin. (P0
0
–P0
7
and P1
0
–P1
5
use
bit 0 of port P0, P1 direction registers respectively.)
When “1” is written to that bit, that pin becomes an output pin.
When “0” is written to the bit corresponding to a pin, that pin be-
comes an input pin.
If data is read from a pin set to output, the value of the port output
latch is read, not the value of the pin itself. Pins set to input are
floating and the value of that pin can be read. If a pin set to input
is written to, only the port output latch is written to and the pin re-
mains floating.
Port P3 Output Control Register
Bit 0 of the port P3 output control register (address 0007
16
) en-
ables control of the output of ports P3
0
to P3
7
.
When the bit is set to “1”, the port output function is valid.
When resetting, bit 0 of the port P3 output control register is set to
“0” (the port output function is invalid.) and ports P3
0
to P3
7
are
pulled up.
Pull-up Control
By setting the PULL register A (address 0016
16
) or the PULL reg-
ister B (address 0017
16
), ports P0 to P6 can control pull-up with a
program.
However, the contents of PULL register A and PULL register B do
not affect ports programmed as the output ports.
The PULL register A setting is invalid for pins set to segment out-
put on the segment output enable register.
Fig. 9 Structure of PULL register A and PULL register B
P0
0
,
P
0
1
pull-up
P0
2
,
P0
3
pull-up
P0
4
–P0
7
pull-up
P1
0
–P1
3
pull-up
P1
4
,
P1
5
pull-up
P1
6
,
P1
7
pull-up
P2
0
–P2
3
pull-up
P2
4
–P2
7
pull-up
PULL register A
(PULLA : address 0016
16
)
b7
b0
P4
1
–P4
3
pull-up
P4
4
–P4
7
pull-up
P5
0
–P5
3
pull-up
P5
4
–P5
7
pull-up
P6
0
–P6
3
pull-up
P6
4
–P6
7
pull-up
Not used (return “0” when read)
0 : No pull-up
1 : Pull-up
PULL register B
(PULLB : address 0017
16
)
b7
b0
Note :
The contents of PULL register A and PULL register B
do not affect ports programmed as the output port.