HD404629R Datasheet, PDF (112/157 Pages) Renesas Technology Corp – AS Microcomputer Incorporating a DTMF Generator Circuit

HD404629R Series
LCD Output Register 3 (LOR3: $01F): Write-only register used to specify ports R5–R7 as pins SEG9–
SEG20 in 4-pin units (figure 100).
LCD output register 3 (LOR3: $01F)
Bit
Initial value
Read/Write
Bit name
3
2
—
0
—
W
Not used LOR32
1
0
W
LOR31
0
0
W
LOR30
LOR32
0
1
R7₀/SEG17–R7₃/SEG20 mode selection
R7₀-R7₃
SEG17–SEG20
LOR30
0
1
R5₀/SEG9–R5₃/SEG12 mode selection
R5₀-R5₃
SEG9–SEG12
LOR31
0
1
R6₀/SEG13–R6₃/SEG16 mode selection
R6₀-R6₃
SEG13–SEG16
Figure 100 LCD Output Register 3 (LOR3)
Large Liquid-Crystal Panel Drive and V_LCD: To drive a large-capacity LCD, decrease the resistance of
the built-in division resistors by attaching external resistors in parallel, as shown in figure 101.
The size of these resistors cannot be simply calculated from the LCD load capacitance because the matrix
configuration of the LCD complicates the paths of charge/discharge currents flowing through the
capacitors—the resistance will also vary with lighting conditions. This size must be determined by trial-
and-error, taking into account the power dissipation of the device using the LCD, but a resistance of 1 to 10
kΩ would usually be suitable. (Another effective method is to attach capacitors of 0.1 to 0.3 µF.)
Always turn off the power switch (set bit 1 of the LCR to 0) before changing the liquid-crystal drive
voltage (V_LCD).
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