
PCF85176
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NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 27 June 2011
7 of 47
NXP Semiconductors
PCF85176
Universal LCD driver for low multiplex rates
The host microcontroller maintains the 2-line I
2
C-bus communication channel with the
PCF85176. The internal oscillator is enabled by connecting pin OSC to pin V
SS
. The
appropriate biasing voltages for the multiplexed LCD waveforms are generated internally.
The only other connections required to complete the system are the power supplies (V
DD
,
V
SS
, and V
LCD
) and the LCD panel chosen for the application.
7.1 Power-On Reset (POR)
At power-on the PCF85176 resets to the following starting conditions:
All backplane and segment outputs are set to V
LCD
The selected drive mode is: 1:4 multiplex with
1
3
bias
Blinking is switched off
Input and output bank selectors are reset
The I
2
C-bus interface is initialized
The data pointer and the subaddress counter are cleared (set to logic 0)
Display is disabled
Remark:
Do not transfer data on the I
2
C-bus for at least 1 ms after a power-on to allow
the reset action to complete.
7.2 LCD bias generator
Fractional LCD biasing voltages are obtained from an internal voltage divider of three
impedances connected between pins V
LCD
and V
SS
. The center impedance is bypassed
by switch if the
1
2
bias voltage level for the 1:2 multiplex drive mode configuration is
selected.
7.3 LCD voltage selector
The LCD voltage selector coordinates the multiplexing of the LCD in accordance with the
selected LCD drive configuration. The operation of the voltage selector is controlled by the
mode-set command from the command decoder. The biasing configurations that apply to
the preferred modes of operation, together with the biasing characteristics as functions of
V
LCD
and the resulting discrimination ratios (D) are given in
Table 5
.
The resistance of the power lines must be kept to a minimum.
Fig 5.
Typical system configuration
HOST
MICRO-
PROCESSOR/
MICRO-
CONTROLLER
t
r
2C
B
SDA
SCL
OSC
40 segment drives
4 backplanes
LCD PANEL
(up to 160
elements)
PCF85176
A0
A1
A2
SA0
V
DD
V
SS
V
SS
V
DD
V
LCD
013aaa071
R
≤