PCF8566_7 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 07 — 25 February 2009 17 of 48
NXP Semiconductors
PCF8566
Universal LCD driver for low multiplex rates
When display data is transmitted to the PCF8566 the display bytes received are stored in
the display RAM based on the selected LCD drive mode. An example of a 7-segment
numeric display illustrating the storage order for all drive modes is shown in Figure 11.
The RAM storage organization applies equally to other LCD types.
The following applies to Figure 11:
• Static drive mode: the eight transmitted data bits are placed in row 0 to eight
successive display RAM addresses.
• 1:2 multiplex drive mode: the eight transmitted data bits are placed in row 0 and 1 to
four successive display RAM addresses.
• 1:3 multiplex drive mode: the eight transmitted data bits are placed in row 0, 1 and 2 of
three successive addresses, with bit 2 of the third address left unchanged. This last bit
can, if necessary, be controlled by an additional transfer to this address but avoid
overriding adjacent data because always full bytes are transmitted.
• 1:4 multiplex drive mode: the eight transmitted data bits are placed in row 0, 1, 2 and
3 to two successive display RAM addresses.
7.12 Data pointer
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 (see Table 13). After this, the data byte is
stored starting at the display RAM address indicated by the data pointer (see Figure 11).
Once each byte is stored, the data pointer is automatically incremented based on the
selected LCD configuration.
The contents of the data pointer are incremented as follows:
• In static drive mode by eight.
• In 1:2 multiplex drive mode by four.
• In 1:3 multiplex drive mode by three.
• In 1:4 multiplex drive mode by two.
If an I
2
C-bus data access terminates early, the state of the data pointer is unknown.
Consequently, the data pointer must be rewritten prior to further RAM accesses.
Fig 10. Display RAM bit map showing the direct relationship between display RAM
addresses and segment outputs and between bits in a RAM word and backplane
outputs
0
0
1
2
3
1234 1920212223
display RAM addresses (columns)/segment outputs (S)
display RAM bits
(rows)/
backplane outputs
(BP)
mgg389
