HD64F2149 Datasheet, PDF (116/1035 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

3.3 Operating Mode Descriptions
3.3.1 Mode 1
The CPU can access a 64-kbyte address space in normal mode. The on-chip ROM is disabled.
Ports 1 and 2 function as an address bus, port 3 functions as a data bus, and part of port 9 carries
bus control signals. Clearing the ABW bit to 0 in the WSCR register makes port B a data bus.
3.3.2 Mode 2
The CPU can access a 16-Mbyte address space in advanced mode. The on-chip ROM is enabled.
After a reset, single-chip mode is set, and the EXPE bit in MDCR must be set to 1 in order to use
external addresses.
When the EXPE bit in MDCR is set to 1, ports 1, 2 and A function as input ports after a reset.
They can be set to output addresses by setting the corresponding bits in the data direction register
(DDR) to 1. Port 3 functions as a data bus, and part of port 9 carries bus control signals. Clearing
the ABW bit to 0 in the WSCR register makes port B a data bus.
3.3.3 Mode 3
The CPU can access a 64-kbyte address space in normal mode. The on-chip ROM is enabled.
After a reset, single-chip mode is set, and the EXPE bit in MDCR must be set to 1 in order to use
external addresses.
When the EXPE bit in MDCR is set to 1, ports 1 and 2 function as input ports after a reset. They
can be set to output addresses by setting the corresponding bits in the data direction register
(DDR) to 1. Port 3 functions as a data bus, and part of port 9 carries bus control signals. Clearing
the ABW bit to 0 in the WSCR register makes port B a data bus.
In this operating mode, the available amount of on-chip ROM in products with 64 kbytes or more
of ROM is limited to 56 kbytes.
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