HD64F36024 datasheet(84/384 Pages) RENESAS

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Section 3 Exception Handling

Rev. 4.00 Sep. 23, 2005 Page 58 of 354

REJ09B0025-0400

3.5

Usage Notes

3.5.1

Interrupts after Reset

If an interrupt is accepted after a reset and before the stack pointer (SP) is initialized, the PC and

CCR will not be saved correctly, leading to a program crash. To prevent this, all interrupt requests,

including NMI, are disabled immediately after a reset. Since the first instruction of a program is

always executed immediately after the reset state ends, make sure that this instruction initializes

the stack pointer (example: MOV.W #xx: 16, SP).

3.5.2

Notes on Stack Area Use

When word data is accessed, the least significant bit of the address is regarded as 0. Access to the

stack always takes place in word size, so the stack pointer (SP: R7) should never indicate an odd

address. Use PUSH Rn (MOV.W Rn, @–SP) or POP Rn (MOV.W @SP+, Rn) to save or restore

3.5.3

Notes on Rewriting Port Mode Registers

When a port mode register is rewritten to switch the functions of external interrupt pins,

IRQ3,

IRQ0, and WKP5 to WKP0, the interrupt request flag may be set to 1.

Figure 3.4 shows a port mode register setting and interrupt request flag clearing procedure.

When switching a pin function, mask the interrupt before setting the bit in the port mode register.

After accessing the port mode register, execute at least one instruction (e.g., NOP), then clear the

interrupt request flag from 1 to 0.

CCR I bit

Set port mode register bit

Execute NOP instruction

Interrupts masked. (Another possibility

is to disable the relevant interrupt in

interrupt enable register 1.)

After setting the port mode register bit,

first execute at least one instruction

(e.g., NOP), then clear the interrupt

request flag to 0

Interrupt mask cleared

Clear interrupt request flag to 0

←

CCR I bit

←

Figure 3.4 Port Mode Register Setting and Interrupt Request Flag Clearing Procedure

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