Common And Segment Signals - NEC Renesas mPD71312 User Manual

3.7 Common and Segment Signals

Each pixel of the LCD panel turns on when the potential difference between the corresponding common and
segment signals becomes higher than a specific voltage (LCD drive voltage, V
potential difference becomes lower than V
Applying DC voltage to the common and segment signals of an LCD panel causes deterioration. To avoid this
problem, this LCD panel is driven by AC voltage.
(1) Common signals
Each common signal is selected sequentially according to a specified number of time slices at the timing
listed in Table 3-4. In the static display mode, the same signal is output to COM0 to COM3.
In the two-time-slice mode, leave the COM2 and COM3 pins open. In the three-time-slice mode, leave the
COM3 pin open.
Number of Time Slices
Static display mode
Two-time-slice mode
Three-time-slice mode
Four-time-slice mode
(2) Segment signals
(a) 52-pin product
The segment signals correspond to 36 bytes of LCD display data memory (00H to 23H of LCDSEG). Bits 0,
1, 2, and 3 of each byte are read in synchronization with COM0, COM1, COM2, and COM3, respectively. If a
bit is 1, it is converted to the select voltage, and if it is 0, it is converted to the deselect voltage. The
conversion results are output to the segment pins (S0 to S35).
(b) 64-pin product
The segment signals correspond to 40 bytes of LCD display data memory (00H to 27H of LCDSEG). Bits 0,
1, 2, and 3 of each byte are read in synchronization with COM0, COM1, COM2, and COM3, respectively. If a
bit is 1, it is converted to the select voltage, and if it is 0, it is converted to the deselect voltage. The
conversion results are output to the segment pins (S0 to S39).
Check, with the information given above, what combination of front-surface electrodes (corresponding to the
segment signals) and rear-surface electrodes (corresponding to the common signals) forms display patterns
in the LCD display data memory, and write the bit data that corresponds to the desired display pattern on a
one-to-one basis.
LCD display data memory bits 1 to 3, bits 2 and 3, and bit 3 are not used for LCD display in the static display,
two-time slot, and three-time slot modes, respectively. So these bits can be used for purposes other than
display.
LCD display data memory bits 4 to 7 are fixed to 0.
CHAPTER 3 LCD CONTROLLER/DRIVER
.
LCD
Table 3-4. COM Signals
COM Signal COM0
User's Manual U18438EJ2V0UD
). The pixels turn off when the
LCD
COM1 COM2
Open
COM3
Open
Open
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