CHAPTER 5 INTERRUPT/EXCEPTION PROCESSING FUNCTION
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5.3 Maskable Interrupts
Maskable interrupt requests can be masked by interrupt control registers. The V850/SB1 and V850/SB2 have 37
to 40 maskable interrupt sources (see
5.1.1 Features
).
If two or more maskable interrupt requests are generated at the same time, they are acknowledged according to
the default priority. In addition to the default priority, eight levels of priorities can be specified by using the interrupt
control registers, allowing programmable priority control.
When an interrupt request has been acknowledged, the acknowledgement of other maskable interrupts is dis-
abled and the interrupt disabled (DI) status is set.
When the EI instruction is executed in an interrupt servicing routine, the interrupt enabled (EI) status is set which
enables interrupts having a higher priority to immediately interrupt the current service routine in progress. Note that
only interrupts with a higher priority will have this capability; interrupts with the same priority level cannot be nested.
To use multiple interrupts, it is necessary to save EIPC and EIPSW to memory or a register before executing the
EI instruction, and restore EIPC and EIPSW to the original values by executing the DI instruction before the RETI
instruction.
When the WDTM4 bit of the watchdog timer mode register (WDTM) is set to 0, the watchdog timer overflow
interrupt functions as a maskable interrupt (INTWDTM).
5.3.1 Operation
If a maskable interrupt occurs, the CPU performs the following processing, and transfers control to a handler
routine:
(1) Saves the restored PC to EIPC.
(2) Saves the current PSW to EIPSW.
(3) Writes an exception code to the lower half-word of ECR (EICC).
(4) Sets the ID bit of PSW and clears the EP bit.
(5) Loads the corresponding handler address to the PC, and transfers control.
The INT input masked by INTC and the INT input that occurs during the other interrupt servicing (when PSW.NP =
1 or PSW.ID = 1) are internally kept pending. When the interrupts are unmasked, or when PSW.NP = 0 and PSW.ID
= 0 by using the RETI and LDSR instructions, the pending INT is input to start the new maskable interrupt servicing.
How the maskable interrupts are serviced is shown below.
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