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CHAPTER 17 LCD CONTROLLER/DRIVER
User
’
s Manual U14701EJ3V0UD
17.6 Common Signals and Segment Signals
An individual pixel on an LCD panel lights when the potential difference of the corresponding common signal and
segment signal reaches or exceeds a given voltage (depending on the panel), and extinguishes when the potential
difference drops lower than V
LCD
.
(1) Common signals
For common signals, the selection timing order is as shown in Table 17-5 according to the number of time divisions
set, and operations are repeated with these as the cycle. In the static mode, the same signal is output to SCOM0.
With 3-time-division operation, the COM3 pin is left open.
Table 17-5. COM Signals
(2) Segment signals
Segment signals correspond to a 40-byte LCD display RAM (FA00H to FA27H
Note
). Each display data memory
bit 0, bit 1, bit 2, and bit 3 is read in synchronization with the SCOM0/COM0, COM1, COM2 and COM3 timings
respectively, and if the value of the bit is 1, it is converted to the selection voltage. If the value of the bit is 0,
it is converted to the non-selection voltage and output to a segment pin (S0 to S39
Note
).
Consequently, it is necessary to check what combination of front surface electrodes (corresponding to the
segment signals) and rear surface electrodes (corresponding to the common signals) of the LCD display to be
used form the display pattern, and then write bit data corresponding on a one-to-one basis with the pattern to
be displayed.
In addition, because LCD display RAM bits 1 to 3 are not used with the static method, these can be used for
other than display purposes.
LCD display RAM bits 4 to 7 are bits for LCD blinking selection. To use the LCD blinking function, set the relevant
bit to 1.
Note
The segment signal output pins or the area that can be used as the LCD display data vary depending on
the product.
Part Number
Segment Signal Output Pins
Area That Can Be Used as LCD Display Data
μ
PD780316, 780318
S0 to S23
FA00H to FA17H
μ
PD780326, 780328
S0 to S31
FA00H to FA1FH
μ
PD780336, 780338
S0 to S39
FA00H to FA27H
μ
PD78F0338
S0 to S39
(S24 to S31, S32 to S39 are alternate with
P90 to P97 and P80 to P87, respectively)
FA00H to FA27H
(when ports 8 and 9 are used as the segment
signal outputs)
COM Signal
Time Division
Static
3-time division
4-time division
Open
COM0
COM1
COM2
COM3
SCOM0
–
–
–
–
–
–