3820 GROUP USER’S MANUAL
1-14
MITSUBISHI MICROCOMPUTERS
3820 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
I/O PORTS
Direction Registers (ports P2, P4
1
–P4
7
, and
P5–P7)
The 3820 group has 43 programmable I/O pins arranged in seven
I/O ports (ports P0–P2 and P4–P7). The I/O ports P2, P4
1
–P4
7
,
and P5–P7 have direction registers which determine the input/out-
put direction of each individual pin. Each bit in a direction register
corresponds to one pin, each pin can be set to be input port or
output port.
When “0” is written to the bit corresponding to a pin, that pin be-
comes an input pin. When “1” is written to that bit, that pin be-
comes an output 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. If a pin set to input is written to, only the port output latch
is written to and the pin remains floating.
Direction Registers (ports P0 and P1)
Ports P0 and P1 have direction registers which determine the in-
put /output direction of each individual port.
Each port in a direction register corresponds to one port, each
port can be set to be input or output.
When “0” is written to the bit 0 of a direction register, that port be-
comes an input port. When “1” is written to that port, that port be-
comes an output port.
Bits 1 to 7 of ports P0 and P1 direction registers are not used.
Ports P3 and P4
0
These ports are only for input.
Pull-up/Pull-down Control
By setting the PULL register A (address 0016
16
) or the PULL reg-
ister B (address 0017
16
), ports except for port P4
0
can control ei-
ther pull-down or pull-up (pins that are shared with the segment
output pins for LCD are pull-down; all other pins are 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.
Fig. 11 Structure of PULL register A and PULL register B
PULL register A
(PULLA : address 0016
16
)
0 : No pull-up (no pull-down)
1 : Pull-up (pull-down)
7
0
Note
: For ports set for the output mode,
pull-up or pull-down is impossible.
PULL register B
(PULLB : address 0017
16
)
7
0
P0
0
–P0
7
pull-down
P1
0
–P1
7
pull-down
P2
0
–P2
7
pull-up
P3
0
–P3
7
pull-down
P7
0
, P7
1
pull-up
Not used (return "0" when read)
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
1
pull-up
Not used (return "0" when read)