R8CSLASH2G datasheet(83/344 Pages) RENESAS

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R8C/2G Group

7. Comparator

Rev.1.00

Apr 04, 2008

Page 63 of 318

REJ09B0387-0100

7.6

Adjusting Internal Reference Voltage (Vref)

The level of the internal reference voltage (Vref) can be adjusted with the value of the BGRTRM register. The

values for correcting the Vref are stored in registers BGRTRMA and BGRTRMB before shipping the MCU. The

value of the BGRTRMA register is the same as that of the BGRTRM register after reset.

To use separate correction values to match the supply voltage ranges, transfer them from registers BGRTRMA and

BGRTRMB to the BGRTRM register. Figure 7.16 shows the Procedure for Adjusting Internal Reference Voltage

(Vref).

When the BGRCR0 bit in the BGRCR register to 1 (disabled), the internal reference voltage (Vref) adjustment

circuit (BGR trimming circuit) is disabled and the value of the BGRTRM register is also disabled.

When the BGR trimming circuit is disabled, the accuracy of the internal reference voltage (Vref) is not guaranteed.

Disable voltage detection circuits 0 to 2 and disable comparators 1 and 2 with the internal reference voltage

selected. The high-speed on-chip oscillator should also be stopped as necessary because the precision of its

oscillation frequency is not also guaranteed.

Figure 7.16

Procedure for Adjusting Internal Reference Voltage (Vref)

Start adjusting the internal reference voltage

(Vref)

Determine the supply voltage(1)

Wait for 10

µs

Vcc

≥ 3.6 V ?

Adjustment of the internal reference voltage

(Vref) completed

Yes

Transfer the value of the BGRTRMA register

to the BGRTRM register

Transfer the value of the BGRTRMB register

to the BGRTRM register

NOTE:

1. The supple voltage can be determined by reading the monitor flag (VCA13 bit in VCA1

Reference Voltage (Vref) (Voltage Detection 2 Used for Determining Supply Voltage).

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