uPD789074 Subseries 8-Bit Single-Chip Microcontrollers UD - Home

CHAPTER 4 PORT FUNCTIONS4.2.4 Port 3This is a 2-bit I/O port with an output latch. Port 3 can be set to input or output mode in 1-bit units by using portmode register 3 (PM3). When P30 and P31 are used as input port pins, on-chip pull-up resistors can be connected in2-bit units by setting pull-up resistor option register 0 (PU0).Port 3 is also used for timer output and buzzer output.RESET input sets port 3 to input mode.Figure 4-9 shows a block diagram of port 3.Figure 4-8. Block Diagram of P30 and P31VDDWRPU0RDPU03P-chInternal busWRPORTWRPMOutput latch(P30, P31)SelectorP30/TO90P31/BZO90PM30, PM31AlternatefunctionPU0: Pull-up resistor option register 0PM: Port mode registerRD: Port 3 read signalWR: Port 3 write signal70User’s Manual U14801EJ3V1UD