pcf8534ah-1 NXP Semiconductors, pcf8534ah-1 Datasheet - Page 13

• Manufacturer Part Number: pcf8534ah-1
• Description: Universal Lcd Driver For Low Multiplex Rates
• Manufacturer: NXP Semiconductors

Philips Semiconductors
6.5
6.5.1
The internal logic and the LCD drive signals of the
PCF8533 are timed either by the built-in oscillator or from
an external clock. When the internal oscillator is used, pad
OSC should be connected to V
from pad CLK provides the clock signal for cascaded
PCF8533s in the system. After power-up, SDA must be
HIGH to guarantee that the clock starts.
6.5.2
The condition for external clock is made by tying pad OSC
to V
The clock frequency (f
frequency.
A clock signal must always be supplied to the device;
removing the clock may freeze the LCD in a DC state.
6.6
The timing of the PCF8533 organizes 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 synchronization signal
(SYNC) maintains the correct timing relationship between
the PCF8533s in the system. The timing also generates
the LCD frame frequency which it derives as an integer
division of the clock frequency (see Table 3). The frame
frequency is a fixed division of the internal clock or of the
frequency applied to pad CLK when an external clock is
used.
6.7
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 one column of the
display RAM.
1999 Jul 30
Universal LCD driver for low multiplex rates
DD
; pad CLK then becomes the external clock input.
Oscillator
Timing
Display register
I
E
NTERNAL CLOCK
XTERNAL CLOCK
CLK
) determines the LCD frame
SS
. In this event, the output
13
6.8
The LCD drive section includes 80 segment outputs
(S0 to S79) which should be connected directly to the
LCD. The segment output signals are generated in
accordance with the multiplexed backplane signals and
with data resident in the display latch. When less than
80 segment outputs are required the unused segment
outputs should be left open-circuit.
6.9
The LCD drive section includes four backplane outputs
BP0 to BP3 which should 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. In the 1 : 2 multiplex drive mode
BP0 and BP2, BP1 and BP3 respectively carry the same
signals and may also be paired to increase the drive
capabilities. In the static drive mode the same signal is
carried by all four backplane outputs and they can be
connected in parallel for very high drive requirements.
6.10
The display RAM is a static 80
LCD data. A logic 1 in the RAM bit map indicates the
on-state of the corresponding LCD segment; similarly, a
logic 0 indicates the off-state. There is a one-to-one
correspondence between the RAM addresses and the
segment outputs, and between the individual bits of a RAM
word and the backplane outputs. The first RAM column
corresponds to the 80 segments operated with respect to
backplane BP0 (see Fig.8). In multiplexed LCD
applications the segment data of the second, third and
fourth column of the display RAM are time-multiplexed
with BP1, BP2 and BP3 respectively.
Segment outputs
Backplane outputs
Display RAM
4-bit RAM which stores
Product specification
PCF8533