UPD784938 Datasheet, PDF (603/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 24 LOCAL BUS INTERFACE FUNCTION
The local bus interface function is provided for the connection of external memory (ROM and RAM) and I/Os.
External memory (ROM and RAM) and I/Os are accessed using the RD, WR, and ASTB pin signals, with pins AD0 to
AD7 used as the multiplexed address/data bus and pins A8 to A19 as the address bus.
The basic bus interface timing is shown in Figures 24-6 and 24-7.
Also provided are a wait function for interfacing with low-speed memory, a refresh signal output function for refreshing
pseudo-static RAM, and a bus hold function for connecting devices that have a bus master function, such as a DMA
controller.
24.1 Memory Expansion Function
With the µPD784938, external memory and I/O expansion can be performed by setting the memory expansion mode
register (MM).
24.1.1 Memory expansion mode register (MM)
MM is an 8-bit register that performs external expansion memory control, address wait number specification, and internal
fetch cycle control.
MM can be read or written to with an 8-bit manipulation instruction or bit manipulation instruction. The MM format is
shown in Figure 24-1.
RESET input sets MM to 20H.
Preliminary User’s Manual U13987EJ1V0UM00
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