UPD784218 Datasheet, PDF (52/92 Pages) NEC – 16-/8-BIT SINGLE-CHIP MICROCONTROLLERS

µPD784218, 784218Y
10.1 Memory Expansion
External program memory and data memory can be connected in two stages: 256 KB and 1 MB.
To connect the external memory, ports 4 through 6 and port 8 are used.
The external memory can be connected in the following two modes:
• Multiplexed bus mode: The external memory is connected by using a time-division address/data bus. The
number of ports used when the external memory is connected can be reduced in this
mode.
• Separate bus mode: The external memory is connected by using an address bus and data bus independent
of each other. Because an external latch circuit is not necessary, this mode is useful
for reducing the number of components and mounting area on the printed wiring board.
10.2 Programmable Wait
Wait state(s) can be inserted to the memory space (00000H through FFFFFH) while the RD and WR signals are
active.
In addition, there is an address wait function that extends the active period of the ASTB signal to gain the address
decode time.
10.3 External Access Status Function
An active-low external access status signal is output from the P37/EXA pin. This signal informs other devices
that are connected with external buses of the external access status, prohibits other devices from outputting data
to an external bus, and enables receive operations.
The external access status signal is output during external accessing.
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Data Sheet U12304EJ2V0DS00