DS72011RB120FPV datasheet(141/1196 Pages) RENESAS

141 / 1196 page

Section 5 Exception Handling

Rev. 2.00 Sep. 07, 2007 Page 113 of 1164

REJ09B0321-0200

5.10

Usage Notes

5.10.1

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 handling.

5.10.2

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 handling.

5.10.3

Address Errors Caused by Stacking of Address Error Exception Handling

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

exception handling (interrupts, etc.) and address error exception handling will start up as soon as

the first exception handling is ended. Address errors will then also occur in the stacking for this

address error exception handling. To ensure that address error exception handling does not go into

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

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

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

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

decremented by 4 for both, so the value of SP will not be a multiple of four after the stacking

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

occurred is itself output. This means the write data stacked will be undefined.

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