Chapter 23 External Device Expansion Function; External Device Expansion Functions; Pin Functions In External Memory Expansion Mode; State Of Port 4 To Port 6 Pins In External Memory Expansion Mode - NEC PD78076 User Manual

Pd78078 series; pd78078y series 8-bit single-chip microcontrollers

Table of Contents

CHAPTER 23 EXTERNAL DEVICE EXPANSION FUNCTION

The external device expansion functions connect external devices to areas other than the internal ROM, RAM,

The external device expansion function can be used in the following two modes:

• Multiplexed bus mode

• Separate bus mode

(1) Multiplexed bus mode

External devices are connected via the multiplexed address/data bus. Connecting external devices using

this mode may reduce the number of ports to be used. In this mode, ports 4 through 6 are used for control

of address/data, reafd/write strobe, wait, address strobe as shown below.

Table 23-1. Pin Functions in External Memory Expansion Mode

Pin function at external device connection

Table 23-2. State of Port 4 to Port 6 Pins in External Memory Expansion Mode

Ports and bits

Single-chip mode

256-byte expansion mode

4-Kbyte expansion mode

16-Kbyte expansion mode

Full address mode

Caution When the external wait function is not used, the WAIT pin can be used as a port in all modes.

Multiplexed address/data bus

Upper Address bus

Read strobe signal

Write strobe signal

Address strobe signal

Address/data

Address/data

Alternate function

RD, WR, WAIT, ASTB