UPD784938 Datasheet, PDF (614/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 24 LOCAL BUS INTERFACE FUNCTION
24.1.3 Basic operation of local bus interface
The local bus interface accesses external memory using ASTB, RD, WR, an address/data bus (AD0 to AD7), and address
bus (A8 to A19). When the local bus interface is used, P64, P65, and port 4 automatically operate as RD, WR and AD0
to AD7. On the address bus, only the pins that correspond to the expansion memory size operate as address bus pins.
An outline of the memory access timing is shown in Figures 24-6 and 24-7.
Figure 24-6. Read Timing
A8 to A19^Note
(output)
High address
AD0 to AD7
Hi-Z
Low address
Hi-Z
Data (input)
Hi-Z
(output)
ASTB (output)
RD (output)
Note The number of address bus pins used depends on the expansion mode size.
Figure 24-7. Write Timing
A8 to A19^Note
(output)
High address
Hi-Z
Hi-Z
AD0 to AD7 (output)
Low address
Hi-Z
Data
ASTB (output)
WR (output)
Note The number of address bus pins used depends on the expansion mode size.
614
Preliminary User’s Manual U13987EJ1V0UM00