Datasheet

71M6543F/71M6543G Data Sheet
62 v2
When using the VLCD boost circuit, use care when setting the LCD_DAC[4:0] (I/O RAM 0x240D[4:0])
value to ensure that the LCD manufacturer’s recommended operating voltage specification is not
exceeded.
The voltage doubler is active in all LCD modes including the LCD mode when LCD_BSTE = 1. Current
dissipation in LCD mode can be reduced if the boost circuit is disabled and the LCD system is operated
directly from VBAT.
The LCD DAC uses a low-power reference and, within the constraints of VBAT and the voltage doubler,
generates a VLCD voltage of 2.65 VDC + 2.65 * LCD_DAC[4:0]/31. Two fuse bytes increase the accuracy
of the LCD_DAC. LCDADJ12 and LCDADJ0 indicate the actual VLCD output voltage when the DAC is
programmed to 12 and 0 respectively.
The LCD_BAT (I/O RAM 0x2402[7]) bit causes the LCD system to use the battery voltage in all power
modes. This may be useful when an external supply is available for the LCD system. The advantage of
connecting the external supply to VBAT, rather than VLCD is that the LCD DAC is still active.
If LCD_EXT = 1, the VLCD pin must be driven from an external source. In this case, the LCD DAC has
no effect.
The LCD system has the ability to drive up to six segments per SEG driver. If the display is configured with
six back planes, the 6-way multiplexing reduces the number of SEG pins required to drive a display and
therefore enhances the number of DIO pins available to the application. Refer to the LCD_MODE[2:0] field
(I/O RAM 0x2400[6:4]) settings (Table 52) for the different LCD multiplexing choices. If 5-state multiplexing
is selected, SEGDIO27 is converted to COM4. If 6-state multiplexing is selected, SEGDIO26 is converted
to COM5. These conversions override the SEG/DIO mapping of SEGDIO26 and SEGDIO27. Additionally,
independent of LCD_MODE[2:0], if LCD_ALLCOM = 1 (I/O RAM 0x2400[3]), then SEGDIO26 and
SEGDIO27 become COM4 and COM5 if their LCD_MAP[ ] bits are set.
The LCD_ON (I/O RAM 0x240C[0]) and LCD_BLANK (I/O RAM 0x240C[1]) bits are an easy way to either
blank the LCD display or turn it fully on. Neither bit affects the contents of the LCD data stored in the
LCDSEG_DIO[ ] registers. In comparison, LCD_RST (I/O RAM 0x240C[2]) clears all LCD data to zero.
LCD_RST affects only pins that are configured as LCD.
A small amount of power can be saved by programming the LCD frequency to the lowest value that
provides satisfactory LCD visibility over the required temperature range.
Table 52 shows all I/O RAM registers that control the operation of the LCD interface.