PCF8534A Datasheet, PDF (30/41 Pages) NXP Semiconductors – Universal LCD driver for low multiplex rates

NXP Semiconductors
SDA
SCL
t _BUF
t _LOW
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SDA
t _HD;STA
t_r
t _HD;DAT
t _HIGH
t _SU;DAT
Fig 19. I²C-bus timing waveforms
t _SU;STA
t _SU;STO
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12. Application information
12.1 Cascaded operation
In large display configurations, up to 16 PCF8534As can be distinguished on the same
I²C-bus by using the 3-bit hardware subaddress (A0, A1 and A2) and the programmable
I²C-bus slave address (SA0). When cascaded PCF8534As are synchronized they can
share the backplane signals from one of the devices in the cascade. Such an
arrangement is cost-effective in large LCD applications since the backplane outputs of
only one device need to be through-plated to the backplane electrodes of the display. The
other PCF8534As of the cascade contribute additional segment outputs but their
backplane outputs are left open-circuit (see Figure 20).
The SYNC line is provided to maintain the correct synchronization between all cascaded
PCF8534As. This synchronization is guaranteed after the power-on reset. The only time
that SYNC is likely to be needed is if synchronization is accidentally lost (e.g. by noise in
adverse electrical environments, or by the definition of a multiplex mode when
PCF8534As with different SA0 levels are cascaded). SYNC is organized as an input /
output pin; the output selection being realized as an open-drain driver with an internal
pull-up resistor. A PCF8534A asserts the SYNC line at the onset of its last active
backplane signal and monitors the SYNC line at all other times. If synchronization in the
cascade is lost, it is restored by the first PCF8534A to assert SYNC. The timing
relationship between the backplane waveforms and the SYNC signal for the various drive
modes of the PCF8534A are shown in Figure 21.
The contact resistance between the SYNC pins of cascaded devices must be controlled. If
the resistance is too high then the device will not be able to synchronize properly.
Table 21 shows the limiting values for contact resistance.
PCF8534A_0
Product data sheet
Rev. 00.90 — 4 February 2008
© NXP B.V. 2008. All rights reserved.
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