SH7708 datasheet(107/633 Pages) RENESAS

107 / 633 page

4.4

Exception Handler Operation

4.4.1

Reset

The reset sequence is used to power up or restart the SH7708 Series from the initialization state.

The

RESET signal is sampled every clock cycle, and in the case of a power-on reset, all

processing being executed (excluding the RTC) is suspended, all unfinished events are canceled,

and reset processing is executed immediately. In the case of a manual reset, however, processing

to retain external memory contents is continued. The

BREQ (bus request) signal is used to

distinguish between a power-on reset (high-level input) and manual reset (low-level input). The

reset sequence consists of the following operations:

• The MD bit in SR is set to 1 to place the SH7708 Series in privileged mode.

• The BL bit in SR is set to 1, masking any subsequent exceptions.

• The RB bit in SR is set to 1.

• An encoded value of H'000 in a power-on reset or H'020 in a manual reset is written to bits 11–

0 of the EXPEVT register to identify the exception event.

• Instruction execution jumps to the user-written exception handler at address H'A0000000.

4.4.2

Interrupts

An interrupt processing request is accepted on completion of the current instruction. The interrupt

acceptance sequence consists of the following operations:

• The contents of the PC and SR are saved in SPC and SSR, respectively.

• The BL bit in SR is set to 1, masking any subsequent exceptions.

• The MD bit in SR is set to 1 to place the SH7708 Series in privileged mode.

• The RB bit in SR is set to 1.

• An encoded value identifying the exception event is written to bits 11–0 of the INTEVT

• Instruction execution jumps to the vector location designated by the sum of the value of the

contents of the vector base register (VBR) and H'00000600 to invoke the exception handler.

4.4.3

General Exceptions

When the SH7708 Series encounters any exception condition other than a reset or interrupt

request, it executes the following operations:

• The contents of the PC and SR are saved in the SPC and SSR, respectively.

• The BL bit in SR is set to 1, masking any subsequent exceptions.

• The MD bit in SR is set to 1 to place the SH7708 Series in privileged mode.

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