PCF85162 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 5 — 17 December 2014 20 of 53
NXP Semiconductors
PCF85162
32 × 4 universal LCD driver for low multiplex rates
7.6 Display RAM
The display RAM is a static 32 4-bit RAM which stores LCD data. There is a one-to-one
correspondence between
• the bits in the RAM bitmap and the LCD segments/elements
• the RAM columns and the segment outputs
• the RAM rows and the backplane outputs.
A logic 1 in the RAM bitmap indicates the on-state of the corresponding LCD element;
similarly, a logic 0 indicates the off-state.
The display RAM bitmap, Figure 11
, shows the rows 0 to 3 which correspond with the
backplane outputs BP0 to BP3, and the columns 0 to 31 which correspond with the
segment outputs S0 to S31. In multiplexed LCD applications the segment data of the first,
second, third, and fourth row of the display RAM are time-multiplexed with BP0, BP1,
BP2, and BP3 respectively.
When display data is transmitted to the PCF85162, the display bytes received are stored
in the display RAM in accordance with the selected LCD drive mode. The data is stored as
it arrives and depending on the current multiplex drive mode the bits are stored singularly,
in pairs, triples or quadruples. To illustrate the filling order, an example of a 7-segment
numeric display showing all drive modes is given in Figure 12
; the RAM filling organization
depicted applies equally to other LCD types.
• In static drive mode the eight transmitted data bits are placed into row 0 as one byte
• In 1:2 multiplex drive mode the eight transmitted data bits are placed in pairs into
row 0 and 1 as four successive 2-bit RAM words
• In 1:3 multiplex drive mode the eight bits are placed in triples into row 0, 1, and 2 as
three successive 3-bit RAM words, with bit 3 of the third address left unchanged. It is
not recommended to use this bit in a display because of the difficult addressing. This
last bit may, if necessary, be controlled by an additional transfer to this address, but
care should be taken to avoid overwriting adjacent data because always full bytes are
transmitted (see Section 7.6.4
)
• In 1:4 multiplex drive mode, the eight transmitted data bits are placed in quadruples
into row 0, 1, 2, and 3 as two successive 4-bit RAM words
The display RAM bitmap shows the direct relationship between the display RAM column and the
segment outputs; and between the bits in a RAM row and the backplane outputs.
Fig 11. Display RAM bitmap
GLVSOD\5$0DGGUHVVHVVHJPHQWRXWSXWV6
FROXPQV
GLVSOD\5$0URZV
EDFNSODQHRXWSXWV
%3
URZV
DDF
