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Revision 1.01

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AS1120

Data Sheet

Shift Register

6 Detailed Description

The AS1120 can drive up to 46 LCD segments and multiple AS1120 devices can be cascaded (see Figure 7 on page

8) to increase the number of LCD segments.

Note: Due to the accurate delay balance between the backplane input, backplane output, and the LCD segments, it

is possible to mix segments of different display crystal types.

Shift Register

Data accesses are made serially via pins DATAIN and CLKIN. At each CLKIN rising edge the signal present at DATAIN

pin is shifted in the first bit of the internal shift register and the other bits are shifted ahead of the first bit.

To cascade multiple AS1120 devices (see Figure 7 on page 8), the last bit of the internal shift register is presented at

pin DATAOUT at the falling edge of the same CLKIN pulse. The LSB is entered first while MSB is the last bit to be

shifted into the shift register.

Note: The shift register is cleared at when the AS1120 is reset.

Latch Register and Error

When a signal is applied at pin LOAD, data present in the shift register is latched into the internal latch register and

presented to the LCD output segments (LCD[0:45]), also passing through an XOR gate with the backplane signal

(BPLIN). The XOR function is necessary to generate the appropriate signals to drive the LCD segments.

Note: At reset the latch register is cleared, thus no LCD segment will be active at power-on.

Synchronous Mode

Data is shifted into the internal shift register at the rising edge of the CLKIN signal. To load the shift register all 46 data

bits are clocked into the register at the rising edge of CLKIN (see Figure 3). The LOAD signal has to be set high for 8

CLKIN periods before the end of the 46 bits. The display will be updated at the 8th CLKIN rising edge after LOAD goes

high as is shown in Figure 3.

Note: During synchronous mode, a clock on BPLIN must be applied to avoid the risk of damaging the LCD crystal.

Figure 3. Synchronous Mode Timing Diagram

46 CLKIN Cycles

8 CLKIN Cycles

LOAD

DATAIN

X

X

LD45 LD44LD43

LD0

LD1

LD2

LD3

LD4

LD5

LD6

LD7

LD8

LD9

LD10

BPLIN

CLKIN

Stop

Display

Update