PCF8577CT Philips Semiconductors, PCF8577CT Datasheet - Page 5

• Manufacturer Part Number: PCF8577CT
• Description: LCD direct/duplex driver with I2C-bus interface
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6
6.1
The hardware subaddress lines A0, A1 and A2 are used to
program the device subaddress for each PCF8577C
connected to the I
OSC and BP2 respectively to reduce pin-out
requirements.
1. Line A0 is defined as LOW (logic 0) when this pin is
2. Line A1 must be defined as LOW (logic 0) or as HIGH
3. In the direct drive mode the second backplane signal
4. In the duplex drive mode the second backplane signal
6.2
The PCF8577C has a single-pin built-in oscillator which
provides the modulation for the LCD segment driver
outputs. One external resistor and one external capacitor
are connected to the A0/OSC pin to form the oscillator (see
Figs 15 and 16). For correct start-up of the oscillator after
power on, the resistor and capacitor must be connected to
the same V
containing more than one PCF8577C the backplane
signals are usually common to all devices and only one
oscillator is required. The devices which are not used for
the oscillator are put into the cascade mode by connecting
the A0/OSC pin to either V
required state for A0. In the cascade mode each
PCF8577C is synchronized from the backplane signal(s).
1998 Jul 30
LCD direct/duplex driver with
I
2
used for the local oscillator or when connected to V
Line A0 is defined as HIGH (logic 1) when connected
to V
(logic 1) by connection to V
BP2 is not used and the A2/BP2 pin is exclusively the
A2 input. Line A2 is defined as LOW (logic 0) when
connected to V
it unconnected (internal pull-down). Line A2 is defined
as HIGH (logic 1) when connected to V
BP2 is required and the A2 signal is undefined. In this
mode device selection is made exclusively from
lines A0 and A1.
FUNCTIONAL DESCRIPTION
C-bus interface
Hardware subaddress A0, A1, A2
Oscillator A0/OSC
DD
.
SS
/V
DD
2
C-bus. Lines A0 and A2 are shared with
as the chip. In an expanded system
SS
or, if this is not possible, by leaving
DD
or V
SS
SS
or V
depending on the
DD
respectively.
DD
.
SS
.
5
6.3
There are nine user-accessible 1-byte registers. The first
is a control register which is used to control the loading of
data into the segment byte registers and to select display
options. The other eight are segment byte registers, split
into two banks of storage, which store the segment data.
The set of even numbered segment byte registers is called
BANK A. Odd numbered segment byte registers are called
BANK B.
There is one slave address for the PCF8577C (see Fig.6).
All addressed devices load the second byte into the control
register and each device maintains an identical copy of the
control byte in the control register at all times (see I
protocol, Fig.7), i.e. all addressed devices respond to
control commands sent on the I
The control register is shown in more detail in Fig.3.
The least-significant bits select which device and which
segment byte register is loaded next. This part of the
register is therefore called the Segment Byte Vector
(SBV).
The upper three bits of the SBV (V5 to V3) are compared
with the hardware subaddress input signals A2, A1
and A0. If they are the same then the device is enabled for
loading, if not the device ignores incoming data but
remains active.
The three least-significant bits of the SBV (V2 to V0)
address one of the segment byte registers within the
enabled chip for loading segment data.
The control register also has two display control bits.
These bits are named MODE and BANK. The MODE bit
selects whether the display outputs are configured for
direct or duplex drive displays. The BANK bit allows the
user to display BANK A or BANK B.
6.4
After each segment byte is loaded the SBV is incremented
automatically. Thus auto-incremented loading occurs if
more than one segment byte is received in a data transfer.
Since the SBV addresses both device and segment
registers in all addressed chips, auto-incremented loading
may proceed across device boundaries provided that the
hardware subaddresses are arranged contiguously.
User-accessible registers
Auto-incremented loading
2
C-bus.
Product specification
PCF8577C
2
C-bus