UPD784938 Datasheet, PDF (529/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 23 INTERRUPT FUNCTIONS
23.2 Interrupt Service Modes
There are three µPD784938 interrupt service modes, as follows:
• Vectored interrupt service
• Macro service
• Context switching
23.2.1 Vectored interrupt service
When an interrupt is acknowledged, the program counter (PC) and program status word (PSW) are automatically saved
to the stack, a branch is made to the address indicated by the data stored in the vector table, and the interrupt service routine
is executed.
23.2.2 Macro service
When an interrupt is acknowledged, CPU execution is temporarily suspended and a data transfer is performed by
hardware. Since macro service is performed without the intermediation of the CPU, it is not necessary to save or restore
CPU statuses such as the program counter (PC) and program status word (PSW) contents. This is therefore very effective
in improving the CPU service time (See 23.8 Macro Service Function).
23.2.3 Context switching
When an interrupt is acknowledged, the prescribed register bank is selected by hardware, a branch is made to a pre-
set vector address in the register bank, and at the same time the current program counter (PC) and program status word
(PSW) are saved in the register bank (see 23.4.2 BRKCS instruction software interrupt (software context switching)
acknowledgment operation and 23.7.2 Context switching).
Remark “Context” refers to the CPU registers that can be accessed by a program while that program is being executed.
These registers include general registers, the program counter (PC), program status word (PSW), and stack
pointer (SP).
Preliminary User’s Manual U13987EJ1V0UM00
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