Renesas Renasas Single-Chip Microcomputer SH7086 Manual de usuario descargar pdf (Pagina 280)

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Chapter 5 Interrupt

5.7 Precautions for Interrupts

5.7.1 Reading address 0000016

Do not read the address 0000016 in a program. When a maskable interrupt request is accepted, the CPU

reads interrupt information (interrupt number and interrupt request priority level) from the address

0000016 during the interrupt sequence. At this time, the IR bit for the accepted interrupt is cleared to “0”.

If the address 0000016 is read in a program, the IR bit for the interrupt which has the highest priority

among the enabled interrupts is cleared to “0”. This causes a problem that the interrupt is canceled, or an

unexpected interrupt request is generated.

5.7.2 Setting the SP

Set any value in the SP(USP, ISP) before accepting an interrupt. The SP(USP, ISP) is cleared to ‘000016’

after reset. Therefore, if an interrupt is accepted before setting any value in the SP(USP, ISP), the pro-

gram may go out of control.

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Especially when using NMI interrupt, set a value in the ISP at the beginning of the program. For the first

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and only the first instruction after reset, all interrupts including NMI interrupt are disabled.

5.7.3 Rewrite the Interrupt Control Register

(1) The interrupt control register for any interrupt should be modified in places where no requests for that

interrupt may occur. Otherwise, disable the interrupt before rewriting the interrupt control register.

(2) To rewrite the interrupt control register for any interrupt after disabling that interrupt, be careful with the

instruction to be used.

Changing any bit other than the IR bit

If while executing an instruction, a request for an interrupt controlled by the register being modified

occurs, the IR bit in the register may not be set to “1” (interrupt requested), with the result that the

interrupt request is ignored. If such a situation presents a problem, use the instructions shown below

to modify the register.

Usable instructions: AND, OR, BCLR, BSET

Changing the IR bit

Depending on the instruction used, the IR bit may not always be cleared to “0” (interrupt not re-

quested). Therefore, be sure to use the MOV instruction to clear the IR bit.

(3) When using the I flag to disable an interrupt, refer to the sample program fragments shown below as

you set the I flag. (Refer to (2) for details about rewrite the interrupt control registers in the sample

program fragments.)

Examples 1 through 3 show how to prevent the I flag from being set to “1” (interrupts enabled) before the

interrupt control register is rewrited, owing to the effects of the internal bus and the instruction queue

buffer.

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Renesas Renasas Single-Chip Microcomputer SH7086 Manual de usuario Pagina 280