SH7101 datasheet(105/560 Pages) RENESAS

105 / 560 page

Section 5 Exception Processing

Rev.1.00 Sep. 18, 2008 Page 71 of 522

REJ09B0069-0100

5.8

Usage Notes

5.8.1

Value of Stack Pointer (SP)

The value of the stack pointer must always be a multiple of four. If it is not, an address error will

occur when the stack is accessed during exception processing.

5.8.2

Value of Vector Base Register (VBR)

The value of the vector base register must always be a multiple of four. If it is not, an address error

will occur when the stack is accessed during exception processing.

5.8.3

Address Errors Caused by Stacking of Address Error Exception Processing

When the value of the stack pointer is not a multiple of four, an address error will occur during

stacking of the exception processing (interrupts, etc.) and address error exception processing will

start after the first exception processing is ended. Address errors will also occur in the stacking for

this address error exception processing. To ensure that address error exception processing does not

go into an endless loop, no address errors are accepted at that point. This allows program control

to be shifted to the service routine for address error exception and enables error processing.

When an address error occurs during exception processing stacking, the stacking bus cycle (write)

is executed. During stacking of the status register (SR) and program counter (PC), the value of SP

is reduced by 4 for both of SR and PC, therefore the value of SP is still not a multiple of four after

the stacking. The address value output during stacking is the SP value, so the address itself where

the error occurred is output. This means that the write data stacked is undefined.

SH7101 Datasheet(PDF) 105 Page - Renesas Technology Corp