2003 Apr 14 8
Philips Semiconductors Product specification
LCD row/column driver for
dot matrix graphic displays
PCF8578
7 FUNCTIONAL DESCRIPTION
The PCF8578 row/column driver is designed for use in one
of three ways:
• Stand-alone row/column driver for small displays
(mixed mode)
• Row/column driver with cascaded PCF8579s
(mixed mode)
• Row driver with cascaded PCF8579s (mixed mode).
7.1 Mixed mode
In mixed mode, the device functions as both a row and
column driver. It can be used in small stand-alone
applications, or for larger displays with up to 15 PCF8579s
(31 PCF8579s when two slave addresses are used).
See Table 1 for common display configurations.
7.2 Row mode
In row mode, the device functions as a row driver with up
to 32 row outputs and provides the clock and
synchronization signals for the PCF8579. Up to 16
PCF8579s can normally be cascaded (32 when two slave
addresses are used).
Timing signals are derived from the on-chip oscillator,
whose frequency is determined by the value of the resistor
connected between OSC and V
SS
.
Commands sent on the I
2
C-bus from the host
microcontroller set the mode (row or mixed), configuration
(multiplex rate and number of rows and columns) and
control the operation of the device. The device may have
one of two slave addresses. The only difference between
these slave addresses is the least significant bit, which is
set by the logic level applied to SA0. The PCF8578 and
PCF8579 also have subaddresses. The subaddress of the
PCF8578 is only defined in mixed mode and is fixed at 0.
The RAM may only be accessed in mixed mode and data
is loaded as described for the PCF8579.
Bias levels may be generated by an external potential
divider with appropriate decoupling capacitors. For large
displays, bias sources with high drive capability should be
used. A typical mixed mode system operating with up to
15 PCF8579s is shown in Fig.5 (a stand-alone system
would be identical but without the PCF8579s).
Table 1 Possible displays configurations
Notes
1. Using 15 PCF8579s.
2. Using 16 PCF8579s.
APPLICATION
MULTIPLEX
RATE
MIXED MODE ROW MODE
TYPICAL APPLICATIONS
ROWS COLUMNS ROWS COLUMNS
Stand alone 1 : 8 8 32 −−small digital or
alphanumerical displays
1:16 16 24 −−
1:24 24 16 −−
1:32 32 8 −−
With PCF8579 1 : 8 8
(1)
632
(1)
8 × 4
(2)
640
(2)
alphanumeric displays and
dot matrix graphic displays
1:16 16
(1)
624
(1)
16 × 2
(2)
640
(2)
1:24 24
(1)
616
(1)
24
(2)
640
(2)
1:32 32
(1)
608
(1)
24
(2)
640
(2)
