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OVERVIEW

7733 Group User’s Manual

1-9

1.3 Pin description

(2) In memory expansion mode

Table 1.3.5 Examples of handling unused pins in memory expansion mode

Pins

P42–P47, P5–P8

____

BHE

(Note 3)

ALE

(Note 4)

_____

HLDA

XOUT (Note 6)

_____

____

HOLD

, RDY

AVcc

AVss, VREF

Handling example

Connect these pins to pin Vcc or Vss via resistors after these

pins are set to the input mode, or leave these pins open after

they are set to the output mode (Notes 1, 2, and 7).

Leave this pin open. (Note 5)

Leave this pin open.

Connect these pins to pin Vcc via resistors after these pins are

set to the input mode. (These pins are pulled high.) (Note 2)

Connect this pin to pin Vcc.

Connect these pins to pin Vss.

Notes 1: When leaving these pins open after they are set to the output mode, note the following: these pins

function as input ports from reset until they are switched to the output mode by software. Therefore,

voltage levels of these pins are undefined and the power source current may increase while these

pins function as input ports. Software reliability can be enhanced when the contents of the above

ports’ direction registers are set periodically. This is because these contents may be changed by

noise, a program runaway which occurs owing to noise, etc.

2: For unused pins, use the shortest possible wiring (within 20 mm from the microcomputer’s pins).

3: This is applied when “H” level is input to pin BYTE.

4: This is applied when “H” level is input to pin BYTE and the accessible area has a capacity of 64

Kbytes.

5: When Vss level is applied to pin CNVss, note the following: this pin functions as an input port from

reset until the processor mode is switched to the memory expansion mode by software. Therefore,

a voltage level of this pin is undefined and the power source current may increase while this pin

functions as an input port.

6: This is applied when an external clock is input to pin XIN.

7: Set pin P42/

φ1 as pin P42. (Clock φ1 output is disabled.) And then, for this pin, do the same

handling as that for pins P43 to P47 and P5 to P8.

P42–P47, P5–P8

AVss

VREF

HOLD

RDY

Left open

HLDA

Vcc

Vss

AVcc

XOUT



When setting ports to input mode

Left open

P42–P47, P5–P8

AVs

VREF

Left open

Vss

AVcc

XOUT



When setting ports to output mode

Left open

Vcc

BHE

ALE

HOLD

RDY

BHE

ALE

HLDA

Fig. 1.3.2 Examples of handling unused pins in memory expansion mode

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