Datasheet

78K0/Kx2-L CHAPTER 17 INTERRUPT FUNCTIONS
R01UH0028EJ0400 Rev.4.00 632
Sep 27, 2010
17.4.3 Multiple interrupt servicing
Multiple interrupt servicing occurs when another interrupt request is acknowledged during execution of an interrupt.
Multiple interrupt servicing does not occur unless the interrupt request acknowledgment enabled state is selected (IE =
1). When an interrupt request is acknowledged, interrupt request acknowledgment becomes disabled (IE = 0). Therefore,
to enable multiple interrupt servicing, it is necessary to set (1) the IE flag with the EI instruction during interrupt servicing to
enable interrupt acknowledgment.
Moreover, even if interrupts are enabled, multiple interrupt servicing may not be enabled, this being subject to interrupt
priority control. Two types of priority control are available: default priority control and programmable priority control.
Programmable priority control is used for multiple interrupt servicing.
In the interrupt enabled state, if an interrupt request with a priority equal to or higher than that of the interrupt currently
being serviced is generated, it is acknowledged for multiple interrupt servicing. If an interrupt with a priority lower than that
of the interrupt currently being serviced is generated during interrupt servicing, it is not acknowledged for multiple interrupt
servicing. Interrupt requests that are not enabled because interrupts are in the interrupt disabled state or because they
have a lower priority are held pending. When servicing of the current interrupt ends, the pending interrupt request is
acknowledged following execution of at least one main processing instruction execution.
Table 17-5 shows relationship between interrupt requests enabled for multiple interrupt servicing and Figure 17-28
shows multiple interrupt servicing examples.
Table 17-5. Relationship Between Interrupt Requests Enabled for Multiple Interrupt Servicing
During Interrupt Servicing
Maskable Interrupt Request
PR = 0 PR = 1
Multiple Interrupt Request
Interrupt Being Serviced
IE = 1 IE = 0 IE = 1 IE = 0
Software
Interrupt
Request
ISP = 0
{
× × ×
{
Maskable interrupt
ISP = 1
{
×
{
×
{
Software interrupt
{
×
{
×
{
Remarks 1. : Multiple interrupt servicing enabled
2. ×: Multiple interrupt servicing disabled
3. ISP and IE are flags contained in the PSW.
ISP = 0: An interrupt with higher priority is being serviced.
ISP = 1: No interrupt request has been acknowledged, or an interrupt with a lower priority is
being serviced.
IE = 0: Interrupt request acknowledgment is disabled.
IE = 1: Interrupt request acknowledgment is enabled.
4. PR is a flag contained in PR0L, PR0H, PR1L, and PR1H.
PR = 0: Higher priority level
PR = 1: Lower priority level