UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 41

• Manufacturer Part Number: UPD75238GJ
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC [NEC]

(1) Configurations of digital I/O ports
(2) I/O mode setting
(3) Operation of digital I/O ports
When a 1-bit test instruction, 1-bit in-
put instruction, or 4-/8-bit input instruc-
tion is executed
When a 4-/8-bit output instruction is
executed
When a 1-bit output instruction
executed
Fig. 4-2 to Fig. 4-11 show the configurations of the ports.
The I/O mode of each I/O port is set by the port mode register as shown in Fig. 4-12.
Each port functions as an input port when the corresponding bit of the port mode register is set to 0, and
functions as an output port when the same corresponding bit is set to 1.
An 8-bit memory manipulation instruction is used to set port mode register group A or B.
A RESET input clears all bits of each port mode register to 0. This means that the output buffers are set
off, and all ports are placed in the input mode.
When an instruction is executed, the operation of the port and pins depends on the I/O mode setting, as
listed in Table 4-1.
Note Instructions such as SET1/CLR1/MOV1 PORTn.bit, CY
Table 4-1 I/O Port Operations by I/O Instructions
Note
is
Receives data on certain pins.
Transfers data in the accumulator to
the output latch.
The contents of the output latch are
undefined.
Input mode (corresponding bit in the
[Output buffer is off]
mode register is 0)
Output mode (corresponding bit in
Receives the contents of the output
latch.
Outputs data in the accumulator to
output pins.
Changes the output pin state accord-
ing to the instruction.
[Output buffer is on]
the mode register is 1)
PD75238
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