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AS1121

Datasheet - Detailed Descr i pti on

8 Detailed Description

Serial Interface

The AS1121 features a versatile 3-pin (CLK, SDI, and SDO) serial interface, which can be connected to microcontrollers or digital signal proces-

sors in various configurations.

The rising edge of the CLK signal shifts data from pin SDI to the internal register. After all data is clocked in, the serial data is latched into the

internal registers at the rising edge of the LD signal.

Note:

All data is clocked in with the MSB first.

Multiple AS1121 devices can be cascaded by connecting the SDO pin of one device with pin SDI of the next device (see Figure 25 on page 17).

The SDO pin can also be connected to the microcontroller to receive status information from the AS1121. The serial data format is 96-bit or 192-

bit wide, depending on mode of the device (see LD on page 2).

Figure 17. Serial Data Input Timing Diagram

Error Information Output

The open-drain output pin XERR indicates if the device is in one of the two error conditions: overtemperature flag or open LED detect. During

pullup resistor.

If an overtemperature or open LED condition is detected, the internal transistor is switched on, and XERR is pulled to GND. Because XERR is an

This reduces the number of signals needed to report a system error.

To differentiate the overtemperature flag from the open LED detect flag from pin XERR, the open LED detect flag can be masked out by setting

OEN = 1 (see Table 6).

DCn

MSB

GSn

MSB

DCn-1

MSB-1

DCn-1

LSB

DCn

MSB

X

X

DCn

LSB

SID

MSB

X

DCn-1

MSB-1

DCn+1

MSB

GSn

LSB

MODE

SDI

CLK

SDO

LD

Dot Correction Mode

Data Input Cycle

Greyscale Mode

Data Input Cycle

Dot Correction Mode

Data Input Cycle

96

1

1

192

1

2

DCn-1

LSB

DCn-1

MSB