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CHAPTER 3 CPU FUNCTION
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Preliminary User’s Manual U16031EJ2V1UD
3.4.8
Specific registers
Specific registers are registers that are protected from being written with illegal data due to erroneous program
execution, etc. The V850E/ME2 has four specific registers, the power-save control register (PSC) (see 8.6.2 (3)
Power-save control register (PSC)), clock control register (CKC) (see 8.3.1 Clock control register (CKC)), clock
source select register (CKS) (see 8.3.2 Clock source select register (CKS)), and SSCG control register (SSCGC)
(see 8.3.3 SSCG control register (SSCGC)). Disable DMA transfer when writing to a specific register.
There is also the command register (PRCMD), a protection register supporting write operations for specific
registers to avoid an unexpected stoppage of the application system due to erroneous program execution (see 8.6.2
(2) Command register (PRCMD)).
3.4.9
System wait control register (VSWC)
The system wait control register (VSWC) is a register that controls the bus access wait for the on-chip peripheral
I/O registers.
Access to on-chip peripheral I/O registers is made in 3 clocks (without wait), however, in the V850E/ME2 waits may
be required depending on the operation frequency. Set the values described in the table below to the VSWC in
accordance with the operation frequency used.
This register can be read or written in 1-bit or 8-bit units (address: FFFFF06EH, initial value: 77H).
Operation Frequency (fX)
VSWC Setting Value
10.00 MHz
≤ fX ≤ 25.00 MHz
00
25.00 MHz < fX
≤ 34.00 MHz
10
34.00 MHz < fX
≤ 68.00 MHz
11
68.00 MHz < fX
≤ 75.00 MHz
12
75.00 MHz < fX
≤ 103.00 MHz
22
103.00 MHz < fX
≤ 125.00 MHz
23
125.00 MHz < fX
≤ 150.00 MHz
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Remark
If the timing of changing a count value contend with the timing of accessing a register when accessing
a register having status flags that indicate the status of the on-chip peripheral functions (such as
UBnSTR) or a register that indicates the count value of a timer (such as TMCn), the register access is
retried. As a result, it may take a longer time to access an on-chip peripheral I/O register.