TC820
DS21476C-page 22 © 2007 Microchip Technology Inc.
TABLE 5-2: LCD BACKPLANE AND
SEGMENT ASSIGNMENTS
5.13 LCD Source
Although most users will design their own custom LCD,
a standard display for the TC820 (Figure 5-15), Part No.
ST-1355-M1, is available from the following sources:
FIGURE 5-15: Typical TC820 LCD.
5.14 Annunciator Output
The annunciator output is a square wave running
at the backplane frequency (for example, 167Hz when
F
OSC
= 40kHz). The peak-to-peak amplitude is equal to
(V
DD
– V
DISP
). Connecting an annunciator of the LCD
to the annunciator output turns it on; connecting it to its
backplane turns it off.
5.15 LCD Drive Voltage (V
DISP
)
The peak-to-peak LCD drive voltage is equal to (V
DD
–
V
DISP
). In the 40-pin dual in-line package (DIP), V
DISP
is internally connected to DGND, providing a typical
LCD drive voltage of 5V
P-P
.
For applications with a wide temperature range, some
LCDs require that the drive levels vary with temperature
to maintain good viewing angle and display contrast. In
this case, the TC820 44-pin package provides a pin
connection for V
DISP
. Figure 5-16 shows TC820 circuits
that can be adjusted to give a temperature compensa-
tion of about 10mV/°C between V
DD
and V
DISP
. The
diode between GND and V
DISP
should have a low turn
on voltage because V
DISP
cannot exceed 0.3V below
GND.
5.16 Crystal Source
Two sources of the 40kHz crystal are:
40-Pin
(PDIP)
44-Pin
(PQFP)
LCD Display
Pin Number
BP1 BP2 BP3
140 3 LOW
241 4 A4"—"
3 42 5 B4 G4 E4
4 43 6 HIGH C4 D4
544 7 A3F3DP3
61 8 B3G3E3
7 2 9 OVER C3 D3
83 10 A2F2DP2
9 4 11 B2 G2 E2
10 5 12 PEAK C2 D2
11 6 13 A1 F1 DP1
12 7 14 B1 G1 E1
13 8 2,16* — C1 D1
14 9 1 BP1 — BATT
15 10 15 LOW BP2 BP3
* Connect both pins 2 and 16 of LCD to
TC820 BP3 of output.
Crystaloid (USA)
Crystaloid Electronics
P.O. Box 628
5282 Hudson Drive
Hudson, OH 44238
Phone: 216-655-2429
Crystaloid (Europe)
Rep. France
102, rue des Nouvelles
F92150 Suresnes France
Phone: 33-1-42-04-29-25
Fax: 33-1-45-06-46-99
HIGH
LOW
OVER PEAK
BATT
PIN 1
Statek Corp.
512 N. Main St.
Orange, CA 92668
Phone: 714-639-7810
Fax: 714-997-1256
Part #: CX-1V-40.0
SPK Electronics
2F-1, No. 312, Sec, 4, Jen Ai Rd.
Taipei, Taiwan R.O.C.
Phone: (02) 754-2677
Fax: 886-2-708-4124
Part #: QRT-38-40.0kHz
