PCF8576D_11 Datasheet, PDF (16/50 Pages) NXP Semiconductors – Universal LCD driver for low multiplex rates

NXP Semiconductors
PCF8576D
Universal LCD driver for low multiplex rates
7.5 Oscillator
7.5.1 Internal clock
The internal logic of the PCF8576D and its LCD drive signals are timed either by its
internal oscillator or by an external clock. The internal oscillator is enabled by connecting
pin OSC to pin V_SS. If the internal oscillator is used, the output from pin CLK can be used
as the clock signal for several PCF8576Ds in the system that are connected in cascade.
7.5.2 External clock
Pin CLK is enabled as an external clock input by connecting pin OSC to V_DD.
The LCD frame signal frequency is determined by the clock frequency (f_clk).
Remark: A clock signal must always be supplied to the device; removing the clock may
freeze the LCD in a DC state, which is not suitable for the liquid crystal.
7.6 Timing
The PCF8576D timing controls the internal data flow of the device. This includes the
transfer of display data from the display RAM to the display segment outputs. In cascaded
applications, the correct timing relationship between each PCF8576D in the system is
maintained by the synchronization signal at pin SYNC. The timing also generates the LCD
frame signal whose frequency is derived from the clock frequency. The frame signal
frequency is a fixed division of the clock frequency from either the internal or an external
clock:
f_fr
=
-^f-^c---^l--^k
24
.
7.7 Display register
The display latch holds the display data while the corresponding multiplex signals are
generated. There is a one-to-one relationship between the data in the display latch, the
LCD segment outputs and each column of the display RAM.
7.8 Segment outputs
The LCD drive section includes 40 segment outputs S0 to S39 which should be
connected directly to the LCD. The segment output signals are generated in accordance
with the multiplexed backplane signals and with data residing in the display latch. When
less than 40 segment outputs are required, the unused segment outputs should be left
open-circuit.
7.9 Backplane outputs
The LCD drive section includes four backplane outputs BP0 to BP3 which must be
connected directly to the LCD. The backplane output signals are generated in accordance
with the selected LCD drive mode. If less than four backplane outputs are required, the
unused outputs can be left open-circuit.
In the 1:3 multiplex drive mode, BP3 carries the same signal as BP1, therefore these two
adjacent outputs can be tied together to give enhanced drive capabilities.
PCF8576D
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 10 — 14 February 2011
© NXP B.V. 2011. All rights reserved.
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