HD64F2168 Datasheet, PDF (568/874 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer

16.3.8 Bidirectional Data Registers 0 to 15 (TWR0 to TWR15)
TWR0 to TWR15 are sixteen 8-bit readable/writable registers to both the slave processor (this
LSI) and the host processor. In TWR0, however, two registers (TWR0MW and TWR0SW) are
allocated to the same address for both the host address and the slave address. TWR0MW is a
write-only register to the host processor, and a read-only register to the slave processor, while
TWR0SW is a write-only register to the slave processor and a read-only register to the host
processor. When the host and slave processors begin a write, after the respective TWR0 registers
have been written to, access right arbitration for simultaneous access is performed by checking the
status flags to see if those writes were valid. For the registers selected from the host according to
the I/O address, see section 16.3.4, LPC Channel 3 Address Register H, L (LADR3H, LADR3L).
Data transferred in an LPC I/O write cycle is written to the selected register; in an LPC I/O read
cycle, the data in the selected register is transferred to the host.
The initial values of TWR0 to TWR15 are undefined.
Rev. 3.00, 03/04, page 528 of 830