PCF8532 datasheet(17/44 Pages) NXP

17 / 44 page

PCF8532_1

Product data sheet

Rev. 1 — 10 February 2009

17 of 44

NXP Semiconductors

PCF8532

Universal LCD driver for low multiplex rates

7.12 Subaddress counter

The storage of display data is conditioned by the contents of the subaddress counter.

Storage is allowed only when the content of the subaddress counter agree with the

hardware subaddress applied to A0 and A1. The subaddress counter value is deﬁned by

the device-select command. If the content of the subaddress counter and the hardware

subaddress do not match 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 PCF8532 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 54th

display data byte transmitted in 1:3 multiplex mode).

The hardware subaddress must not be changed whilst the device is being accessed on

the I2C-bus interface.

7.13 Output bank selector

The output bank selector selects one of the four bits per display RAM address for transfer

to the display register. The actual bit selected depends on the LCD drive mode in

operation and on the instant in the multiplex sequence.

• In 1:4 multiplex mode, all RAM addresses of bit 0 are selected, these are followed by

the contents of bit 1, bit 2 and then bit 3

• In 1:3 multiplex mode, bits 0, 1 and 2 are selected sequentially

• In 1:2 multiplex mode, bits 0 and 1 are selected

• In the static mode, bit 0 is selected.

The SYNC signal will reset these sequences to the following starting points:

• Bit 3 for 1:4 multiplex mode

• Bit 2 for 1:3 multiplex mode

• Bit 1 for 1:2 multiplex mode

• Bit 0 for static mode

The PCF8532 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 the contents of bit 0. In the 1:2 multiplex 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.

7.14 Input bank selector

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 multiplex drive mode by using the bank-select command. The

input bank selector functions independently to the output bank selector.

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