H8SLASH3021 datasheet(547/712 Pages) RENESAS

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17. Power-Down State

Rev.2.00 Mar. 22, 2007 Page 523 of 684

REJ09B0352-0200

17.6

Module Standby Function

17.6.1

Module Standby Timing

The module standby function can halt several of the on-chip supporting modules (the ITU, SCI0,

SCI1, and A/D converter) independently of the power-down state. This standby function is

controlled by bits MSTOP5 to MSTOP3 and MSTOP0 in MSTCR. When one of these bits is set

to 1, the corresponding on-chip supporting module is placed in standby and halts at the beginning

of the next bus cycle after the MSTCR write cycle.

17.6.2

Read/Write in Module Standby

When an on-chip supporting module is in module standby, read/write access to its registers is

disabled. Read access always results in H'FF data. Write access is ignored.

17.6.3

Usage Notes

When using the module standby function, note the following points.

Cancellation of Interrupt Handling: When an on-chip supporting module is placed in standby

by the module standby function, its registers are initialized, including registers with interrupt

request flags. Consequently, if an interrupt occurs just before the MSTOP bit is set to 1, the

interrupt will not be recognized. The interrupt source will not be held pending.

Pin States: Pins used by an on-chip supporting module lose their module functions when the

module is placed in module standby. What happens after that depends on the particular pin. For

details, see section 7, I/O Ports. Pins that change from the input to the output state require special

care. For example, if SCI1 is placed in module standby, the receive data pin loses its receive data

function and becomes a generic I/O pin. If its data direction bit is set to 1, the pin becomes a data

output pin, and its output may collide with external serial data. Data collisions should be prevented

by clearing the data direction bit to 0 or taking other appropriate action.

function, all its registers are initialized. To restart the module, after its MSTOP bit is cleared to 0,

its registers must be set up again. It is not possible to write to the registers while the MSTOP bit is

set to 1.

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