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

CHAPTER 4 PORT FUNCTIONS4.2.3 Port 2This is an 8-bit I/O port with an output latch. Port 2 can be set to input or output mode in 1-bit units by using portmode register 2 (PM2). For pins P20 to P27, on-chip pull-up resistors can be connected in 1-bit units by setting pullupresistor option register B2 (PUB2).Port 2 is also used for external interrupt input, serial interface I/O, and timer I/O.RESET input sets port 2 to input mode.Figures 4-4 through 4-7 show block diagrams of port 2.Caution When using the pins of port 2 for the serial interface, the I/O and output latches must be setaccording to the function to be used. For details of the settings, see Table 9-2 Operation ModeSettings of Serial Interface 20.Figure 4-4. Block Diagram of P20VDDWRPUB2PUB20P-chAlternatefunctionRDInternal busWRPORTWRPMOutput latch(P20)SelectorP20/ASCK20/SCK20PM20AlternatefunctionPUB2:PM:RD:WR:Pull-up resistor option register B2Port mode registerPort 2 read signalPort 2 write signal66User’s Manual U14801EJ3V1UD