H8SLASH3028F datasheet(78/923 Pages) RENESAS

78 / 923 page

Rev. 2.00, 09/03, page 48 of 890

2.8.2

Program Execution State

In this state the CPU executes program instructions in normal sequence.

2.8.3

Exception-Handling State

The exception-handling state is a transient state that occurs when the CPU alters the normal

program flow due to a reset, interrupt, or trap instruction. The CPU fetches a starting address from

the exception vector table and branches to that address. In interrupt and trap exception handling

the CPU references the stack pointer (ER7) and saves the program counter and condition code

Types of Exception Handling and Their Priority: Exception handling is performed for resets,

interrupts, and trap instructions. Table 2.14 indicates the types of exception handling and their

priority. Trap instruction exceptions are accepted at all times in the program execution state.

Table 2.14 Exception Handling Types and Priority

Priority

Type of Exception

Detection Timing

Start of Exception Handling

High

Reset

Synchronized with clock

Exception handling starts immediately

when

RES changes from low to high

Interrupt

End of instruction

execution or end of

exception handling*

When an interrupt is requested,

exception handling starts at the end of

the current instruction or current

exception-handling sequence

Low

Trap instruction

When TRAPA instruction

is executed

Exception handling starts when a trap

(TRAPA) instruction is executed

Note: * Interrupts are not detected at the end of the ANDC, ORC, XORC, and LDC instructions, or

immediately after reset exception handling.

Figure 2.12 classifies the exception sources. For further details about exception sources, vector

numbers, and vector addresses, see section 4, Exception Handling, and section 5, Interrupt

Controller.

Exception

sources

Reset

Interrupt

Trap instruction

External interrupts

Internal interrupts (from on-chip supporting modules)

Figure 2.12 Classification of Exception Sources

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