UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 141
Manufacturer Part Number
4 BIT SINGLE-CHIP MICROCOMPUTER
5.5 VECTOR ADDRESS SHARE INTERRUPT PROCESSING
(1) When using only one interrupt source
(2) When using both interrupt sources
Since interrupt sources INTBT and INT4 share the vector table, the following two cases must be considered.
The interrupt enable flag corresponding to the required interrupt source of the two interrupt sources
sharing the vector table is set and the other interrupt enable flag is cleared. In this case, the enabled
interrupt source (IE
interrupt request flag is reset. (The same operation as that of interrupts not sharing a vector address)
The interrupt enable flags corresponding to the two interrupt sources are set. In this case, the logical and
of the interrupt request flags corresponding to the two interrupt sources is an interrupt request.
Even if one or both of the interrupt request flags are set and an interrupt request is accepted, neither of
the interrupt request flags is reset.
The interrupt service routine must therefore judge which interrupt source caused an interrupt. This is done
by executing a DI instruction at the beginning of the interrupt service routine and checking the interrupt
request flags with an SKTCLR instruction.
= 1) issues an interrupt request. If this request is accepted, the corresponding