1-13
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
3822 Group
I/O PORTS
Direction Registers (ports P2, P41–P47, and
P5–P7)
The 3822 group has 49 programmable I/O pins arranged in seven
I/O ports (ports P0–P2 and P41–P47 and P5–P7). The I/O ports
P2, P41–P47, and P5–P7 have direction registers which determine
the input/output direction of each individual pin. Each bit in a direc-
tion register corresponds to one pin, each pin can be set to be in-
put 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 P40
These ports are only for input.
Pull-up/Pull-down Control
By setting the PULL register A (address 001616) or the PULL reg-
ister B (address 001716), ports except for port P40 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. 10 Structure of PULL register A and PULL register B
P00–P07 pull-down
P10–P17 pull-down
P20–P27 pull-up
P30–P37 pull-down
P70, P71 pull-up
Not used (return “0” when read)
PULL register A
(PULLA : address 001616)
b7
b0
P41–P43 pull-up
P44–P47 pull-up
P50–P53 pull-up
P54–P57 pull-up
P60, P63 pull-up
P64–P67 pull-up
Not used (return “0” when read)
0 : Disable
1 : Enable
PULL register B
(PULLB : address 001716)
b7
b0
Note : The contents of PULL register A and PULL register B
do not affect ports programmed as the output ports.