NEC V850E/MS1 UPD703100, Руководство пользователя

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CHAPTER 3 CPU FUNCTION
User’s Manual U12688EJ4V0UM00
100
3.4.9 Specific registers
Specific registers are registers that are protected from being written with illegal data due to erroneous program
execution, etc. The write access of these specific registers is executed in a specific sequence, and if abnormal store
operations occur, the system status register (SYS) is notified. The V850E/MS1 has two specific registers, clock
control register (CKC) and the power save control register (PSC). For details of the CKC register, refer to 8.3.3 and
for details of the PSC register, refer to 8.5.2.
The access sequence to the specific registers is shown below.
The following sequence shows the data setting of the specific registers.
<1> Provide data in the desired general-purpose register to be set in the specific register.
<2> Write the general-purpose register prepared in <1> in the command register (PRCMD).
<3> Write to the specific register using the general-purpose register prepared in <1> (do this using the following
instructions).
•
Store instruction (ST/SST instruction)
•
Bit operation instruction (SET1/CLR1/NOT1 instruction)
<4> If the system moves to the IDLE or software STOP mode, insert a NOP instruction (1 instruction).
Example <1> MOV 0x04, r10
<2> ST.B r10, PRCMD [r0]
<3> ST.B r10, PSC [r0]
<4> NOP
No special sequence is required when reading the specific registers.
Caution Do not write to the PRCMD register or to a specific register by DMA transfer.
Remarks 1. A store instruction to a command register will not be received with an interrupt.
This presupposes that this is done with the continuous store instructions in <1> and <2> above in
the program. If another instruction is placed between <1> and <2>, when an interrupt is received by
that instruction, the above sequence may not be established, and cause a malfunction, so caution is
necessary.
2. The data written in the PRCMD register is dummy data, but use the same general-purpose register
for writing to the PRCMD register (<2> in the example above) as was used in setting data in the
specific register (<3> in the example above). Addressing is the same in the case where a general-
purpose register is used.
3. It is necessary to insert 1 or more NOP instructions just after a store instruction to the PSC register
for setting it in the software STOP or IDLE mode. When releasing each power save mode by
interrupt, or when resetting after executing interrupt processing, start execution from the next
instruction without executing the instruction just after the store instruction.