W78ERD2 Datasheet, PDF (33/72 Pages) Winbond – 8-BIT MICROCONTROLLER

W78ERD2
8. PORT 4 AND BASE ADDRESS REGISTERS
Port 4, address E8H, is a 4-bit multipurpose programmable I/O port. Each bit can be configured
individually by software. The Port 4 has four different operation modes.
Mode 0: P4.0 − P4.3 is a bi-directional I/O port which is same as port 1. P4.2 and P4.3 also serve as
external interrupt INT3 and INT2 if enabled.
Mode 1: P4.0 − P4.3 are read strobe signals that are synchronized with RD signal at specified
addresses. These signals can be used as chip-select signals for external peripherals.
Mode 2: P4.0 − P4.3 are write strobe signals that are synchronized with WR signal at specified
addresses. These signals can be used as chip-select signals for external peripherals.
Mode 3: P4.0 − P4.3 are read/write strobe signals that are synchronized with RD or WR signal at
specified addresses. These signals can be used as chip-select signals for external
peripherals.
When Port 4 is configured with the feature of chip-select signals, the chip-select signal address range
depends on the contents of the SFR P4xAH, P4xAL, P4CONA and P4CONB. The registers P4xAH
and P4xAL contain the 16-bit base address of P4.x. The registers P4CONA and P4CONB contain the
control bits to configure the Port 4 operation mode.
P40AH, P40AL:
The Base address register for comparator of P4.0. P40AH contains the high-order byte of address,
P40AL contains the low-order byte of address.
P41AH, P41AL:
The Base address register for comparator of P4.1. P41AH contains the high-order byte of address,
P41AL contains the low-order byte of address.
P42AH, P42AL:
The Base address register for comparator of P4.2. P42AH contains the high-order byte of address,
P42AL contains the low-order byte of address.
P43AH, P43AL:
The Base address register for comparator of P4.3. P43AH contains the high-order byte of address,
P43AL contains the low-order byte of address.
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Publication Release Date: April 20, 2005
Revision A4