PCF8578USLASH2 datasheet(8/44 Pages) PHILIPS

8 / 44 page

1998 Sep 08

Philips Semiconductors

Product speciﬁcation

LCD row/column driver for dot matrix

graphic displays

PCF8578

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 VSS.

Commands sent on the I2C-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

−−

small digital or

alphanumerical displays

1:16

−−

1:24

−−

1:32

−−

With PCF8579

1 : 8

8(1)

632(1)

× 44(2)

640(2)

alphanumeric displays and

dot matrix graphic displays

1:16

16(1)

624(1)

× 2(2)

640(2)

1:24

24(1)

616(1)

24(2)

640(2)

1:32

32(1)

608(1)

24(2)

640(2)

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