UPD75518 NEC, UPD75518 Datasheet - Page 42

• Manufacturer Part Number: UPD75518
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

PD75518(A)
(2) Setting the I/O mode
As shown in Fig. 4-9, the I/O mode for each I/O port is set with the port mode register.
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 bit is set to 1.
An 8-bit memory manipulation instruction is used to set port mode register group A, B, or C.
The generation of a RESET signal clears all the bits of each port mode register to 0. This means that the
output buffers are set off and all ports function in the input mode.
42