PCF8576 Philips Semiconductors, PCF8576 Datasheet - Page 16

• Manufacturer Part Number: PCF8576
• Description: Universal LCD driver for low multiplex rates
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6.12
The addressing mechanism for the display RAM is
realized using the data pointer. This allows the loading of
an individual display data byte, or a series of display data
bytes, into any location of the display RAM. The sequence
commences with the initialization of the data pointer by the
LOAD DATA POINTER command. Following this, an
arriving data byte is stored starting at the display RAM
address indicated by the data pointer thereby observing
the filling order shown in Fig.11. The data pointer is
automatically incremented in accordance with the chosen
LCD configuration. That is, after each byte is stored, the
contents of the data pointer are incremented by eight
(static drive mode), by four (1 : 2 multiplex drive mode) or
by two (1 : 4 multiplex drive mode).
6.13
The storage of display data is conditioned by the contents
of the subaddress counter. Storage is allowed to take
place only when the contents of the subaddress counter
agree with the hardware subaddress applied to A0, A1
and A2. The subaddress counter value is defined by the
DEVICE SELECT command. If the contents of the
subaddress counter and the hardware subaddress do not
agree then data storage is inhibited but the data pointer is
incremented as if data storage had taken place.
The subaddress counter is also incremented when the
data pointer overflows.
The storage arrangements described lead to extremely
efficient data loading in cascaded applications. When a
series of display bytes are sent to the display RAM,
automatic wrap-over to the next PCF8576 occurs when
the last RAM address is exceeded. Subaddressing across
device boundaries is successful even if the change to the
next device in the cascade occurs within a transmitted
character (such as during the 14th display data byte
transmitted in 1 : 3 multiplex mode).
6.14
This selects one of the four bits per display RAM address
for transfer to the display latch. The actual bit chosen
depends on the particular LCD drive mode in operation
and on the instant in the multiplex sequence. In 1 : 4
multiplex, all RAM addresses of bit 0 are the first to be
selected, these are followed by the contents of bit 1, bit 2
and then bit 3. Similarly in 1 : 3 multiplex, bits 0, 1 and 2
are selected sequentially. In 1 : 2 multiplex, bits 0 and 1
are selected and, in the static mode, bit 0 is selected.
1998 Feb 06
Universal LCD driver for low multiplex
rates
Data pointer
Subaddress counter
Output bank selector
16
The PCF8576 includes a RAM bank switching feature in
the static and 1 : 2 multiplex drive modes. In the static
drive mode, the BANK SELECT command may request
the contents of bit 2 to be selected for display instead of
bit 0 contents. In the 1 : 2 drive mode, the contents of
bits 2 and 3 may be selected instead of bits 0 and 1.
This gives the provision for preparing display information
in an alternative bank and to be able to switch to it once it
is assembled.
6.15
The input bank selector loads display data into the display
RAM in accordance with the selected LCD drive
configuration. Display data can be loaded in bit 2 in static
drive mode or in bits 2 and 3 in 1 : 2 drive mode by using
the BANK SELECT command. The input bank selector
functions independent of the output bank selector.
6.16
The display blinking capabilities of the PCF8576 are very
versatile. The whole display can be blinked at frequencies
selected by the BLINK command. The blinking frequencies
are integer multiples of the clock frequency; the ratios
between the clock and blinking frequencies depend on the
mode in which the device is operating, as shown in
Table 4.
An additional feature is for an arbitrary selection of LCD
segments to be blinked. This applies to the static and
1 : 2 LCD drive modes and can be implemented without
any communication overheads. By means of the output
bank selector, the displayed RAM banks are exchanged
with alternate RAM banks at the blinking frequency.
This mode can also be specified by the BLINK command.
In the 1 : 3 and 1 : 4 multiplex modes, where no alternate
RAM bank is available, groups of LCD segments can be
blinked by selectively changing the display RAM data at
fixed time intervals.
If the entire display is to be blinked at a frequency other
than the nominal blinking frequency, this can be effectively
performed by resetting and setting the display enable bit E
at the required rate using the MODE SET command.
Input bank selector
Blinker
Product specification
PCF8576