UPD78F0138 NEC, UPD78F0138 Datasheet - Page 375

• Manufacturer Part Number: UPD78F0138
• Description: (UPD78xxxx) 8-Bit Single-Chip Microcontrollers
• Manufacturer: NEC

interrupt servicing takes place. Before each interrupt request is acknowledged, the EI instruction must always be
issued to enable interrupt request acknowledgment.
than that of INTxx, and multiple interrupt servicing does not take place. The INTyy interrupt request is held pending,
and is acknowledged following execution of one main processing instruction.
Example 1. Multiple interrupt servicing occurs twice
During servicing of interrupt INTxx, two interrupt requests, INTyy and INTzz, are acknowledged, and multiple
Example 2. Multiple interrupt servicing does not occur due to priority control
Interrupt request INTyy issued during servicing of interrupt INTxx is not acknowledged because its priority is lower
PR = 0: Higher priority level
PR = 1: Lower priority level
IE = 0:
Interrupt request acknowledgment disabled
INTxx
(PR = 1)
Main processing
EI
Figure 17-10. Examples of Multiple Interrupt Servicing (1/2)
INTxx
(PR = 0)
1 instruction execution
Main processing
IE = 1
IE = 0
EI
CHAPTER 17 INTERRUPT FUNCTIONS
INTyy
(PR = 0)
INTxx servicing
User’s Manual U16228EJ2V0UD
RETI
EI
IE = 1
INTyy
(PR = 1)
IE = 0
IE = 1
INTxx servicing
IE = 0
IE = 1
IE = 0
RETI
INTzz
(PR = 0)
EI
INTyy servicing
RETI
EI
INTyy servicing
RETI
IE = 1
IE = 0
INTzz servicing
RETI
375