H838024 datasheet(272/697 Pages) RENESAS

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Section 8 I/O Ports

Rev. 7.00 Mar 10, 2005 page 230 of 652

REJ09B0042-0700

Bit 3— P92 to P90 Step-Up Circuit Control (PIOFF)

Bit 3 turns the P92 to P90 step-up circuit on and off. This bit is reserved in the H8/38024S Group

and H8/38124 Group.

Bit 3

PIOFF

Description

Large-current port step-up circuit is turned on

(initial value)

Large-current port step-up circuit is turned off

Note:

In the H8/38024 ZTAT version and mask ROM version, and the HD64F38024R, the

following precautions should be followed when accessing the PIOFF bit.

When turning the voltage boost circuit on or off, always write to the register when the buffer

NMOS is off (port data set to 1). Also, when turning on the voltage boost circuit, first clear

PIOFF to 0 and then after waiting 30 system clock cycles turn on the buffer NMOS (port

data cleared to 0). If 30 system clock cycles have not elapsed the voltage boost circuit will

not start operating and it will not be possible to produce a large current flow, resulting in

unstable operation.

In the HD64F38024, the following precautions should be followed when accessing the

PIOFF bit.

In the HD64F38024, if port data bits are cleared from 1 to 0 while the PIOFF bit is set to 1,

repeated charge-discharge cycles will occur in the voltage boost circuit, causing the current

consumption to rise and fall cyclically. The amount of rise in the current consumption in this

case is between several tens of µA and 100 µA above the normal level. Therefore, the

following points should be kept in mind.

(1) Not Using Subclock

Regardless of whether or not port 9 is used, the PIOFF bit should be left at its initial

value (0) and not changed.

(2) Not Using Port 9

Port data should be used unchanged with the PIOFF bit either at its initial value (0) or

set to 1. In the latter case the current consumption will vary, due to the intermittent

operation of the voltage boost circuit, by about 1 µA (standby mode or watch mode, VCC

= 3.0 V, Ta = 25

°C).

(3) Using Port 9 with PIOFF Always Cleared to 0

This case applies to instances in which the voltage boost circuit is used constantly to

generate a large current glow, or an increase in current consumption due to the

operation of the voltage boost circuit is permissible even in the standby mode or watch

mode (see (2) above). In this case the PIOFF bit should be left at its initial value (0) and

not changed.

(4) Using Port 9 with PIOFF Set to 1

This case applies to instances in which it is necessary to change the value of the PIOFF

bit due to operating conditions or where it is desirable to keep the PIOFF bit set to 1

because no large current is required (for example, shutting down the voltage boost

circuit to reduce current consumption in the watch mode). In this case, clear port data

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