NEC PD750008 Manuale Utente

µPD750008 USER'S MANUAL

The interrupt function can be used more effectively in the ways described below.

By allocating addresses 00H to 7FH as data memory used by the interrupt service routine and specifying

MBE = 0 in an interrupt vector table, the user can code a program without being concerned with a memory

bank.

If a program must use memory bank 1 for some reason, save the memory bank select register using the

PUSH BS instruction before selecting memory bank 1.

The normal routine uses register banks 2 and 3 with RBE = 1 and RBS = 2.  If the interrupt routine is for

one nested interrupt, use register bank 0 with RBE = 0, so that you do not have to save or restore the

registers.  When two or more interrupts are nested, set RBE to 1, save the register bank by using the PUSH

BS instruction, and set RBS to 1 to select register bank 1.

Setting an interrupt request flag using an instruction has the same effect as the occurrence of an interrupt.

Debug operation for irregular interrupts or concurrently occurring interrupts can be performed more

efficiently by setting the interrupt request flags using an instruction.

To use the interrupt function, a main program must:

(a) Set a desired interrupt enable flag (using the EI IExxx instruction)

(b) Select an active edge when INT0 or INT1 is used (set IM0 or IM1)

(c) To use nesting (of an interrupt with the higher priority), set IPS (IME can be set at the same time).

(d) Set the interrupt master enable flag (IME) using the EI instruction

In the interrupt routine, MBE and RBE are set by the vector table.  However, when the interrupt specified

as having the higher priority is processed, the register bank must be saved and set.

To return from the interrupt routine, use the RETI instruction.

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