HD64F38024HV Datasheet, PDF (254/684 Pages) Renesas Technology Corp – Hardware Manual Renesas 8-Bit Single-Chip Microcomputer H8 Family/H8/300L Super Low Power Series

Section 8 I/O Ports
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
0
Large-current port step-up circuit is turned on
(initial value)
1
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
Rev. 8.00 Mar. 09, 2010 Page 232 of 658
REJ09B0042-0800