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CHAPTER 3 CPU
3.10.8 EIT Processing
This section explains the EIT processing.
In the explanation, "transfer-from PC" indicates the address of an instruction where
each EIT source was detected.
"Next instruction address" means that the EIT-detected instruction is as follows:
LDI = 32: PC+6
LDI = 20, COPOP, COPLD, COPST, or COPSV: PC+4
Other instruction: PC+2
s Processing of User Interrupt/NMI
If a user interrupt or user NMI interrupt request is issued, the acceptance of the request is
determined in the following order:
r Determining the acceptance of interrupt request
1. The interrupt levels of requests issued simultaneously are compared and the request of the
highest level (smallest value) is selected. The level of a maskable interrupt is compared with
the value of the corresponding ICR and that of a NMI is compared with a predetermined
constant.
2. If several interrupt requests of the same level are issued, the interrupt request of the smallest
interrupt number is selected.
3. The interrupt level of the selected interrupt request is compared with the level mask value
determined by ILM.
When the interrupt level is equal to or greater than the level mask value, the interrupt
request is masked and not accepted.
When the interrupt level is smaller than the level mask value, go to 4).
4. If the selected interrupt request is maskable, the interrupt request is masked and not
accepted when the I flag is 0. When the I flag is 1, go to 5).
If the selected interrupt request is NMI, go to 5) whether or not the I flag is 0.
5. When the above conditions are satisfied, the interrupt request is accepted at a break of
interrupt processing.
If a user interrupt/NMI request is received at the detection of an EIT request, the CPU effects
the following processing using the interrupt number corresponding to the accepted interrupt
request.
( ) in [Processing] represents an address specified in the register.
[Processing]
SSP-4 --> SSP
PS --> (SSP)
SSP-4 --> SSP
Instruction of next address --> (SSP)
Interrupt level of accepted request --> ILM