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CHAPTER 6 CLOCK GENERATION FUNCTION
User’s Manual U13850EJ6V0UD
198
(2) While an instruction is being executed on external ROM
If the V850/SB1 or V850/SB2 is used under the following conditions, the address indicated by the program
counter (PC) differs from the address that actually reads an instruction after the power save mode has been
released.
Of the instructions 4 to 16 bytes after the instruction that writes data to the PSC register, the CPU may ignore 4
or 8 bytes of the instruction and execute wrong instructions.
Caution
A PC discrepancy occurs only when all the conditions (i) to (iii) in [Conditions] below are met.
It does not occur if even one condition is not met.
[Conditions]
(i)
If the power save mode (IDLE or STOP mode) is set while an instruction is being executed on the external
ROM
(ii) If the power save mode is released by an interrupt request
(iii) If the subsequent instruction is executed while an interrupt request is being held pending after the power
save mode has been released
Conditions in which an interrupt request is held pending:
•
If the NP flag of the PSW register is “1” (during NMI servicing/set by software)
•
If the ID flag of the PSW register is “1” (during interrupt request servicing/DI instruction/set by software)
•
If the power save mode is released by an interrupt request with a priority the same as or lower than the
interrupt request being serviced even though interrupts are enabled (EI status)
Therefore, use the V850/SB1 and V850/SB2 under the following conditions:
[Conditions]
(i)
Do not use a power save mode (IDLE or STOP mode) while an instruction is being executed on the external
ROM
(ii) Take the following measures using software if a power save mode is used while an instruction is being
executed on the external ROM:
•
Insert six NOP instructions 4 bytes after the instruction that writes data to the PSC register.
•
Insert the BR $+2 instruction to eliminate the discrepancy in the address of the PC after the NOP
instructions.