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CAPTURE TEST PATTERNS

ADS6445, ADS6444

ADS6443, ADS6442

SLAS531 – MAY 2007

ADS644X outputs the bit clock (DCLK), positioned nearly at the center of the data transitions. It is recommended

to route the bit clock, frame clock and output data lines with minimum relative skew on the PCB. This ensures

sufficient setup/hold times for a reliable capture by the receiver.

The DESKEW is a 1010... or 0101... pattern output on the serial data lines that can be used to verify if the

receiver capture clock edge is positioned correctly. This may be useful in case there is some skew between

DCLK and serial data inside the receiver. Once deserialized, it is required to ensure that the parallel data is

aligned to the frame boundary. The SYNC test pattern can be used for this. For example, in the 1-wire interface,

the SYNC pattern is 7 '1's followed by 7 '0's (from MSB to LSB). This information can be used by the receiver

logic to shift the deserialized data till it matches the SYNC pattern.

In addition to DESKEW and SYNC, the ADS644X includes other test patterns to verify correctness of the

capture by the receiver such as all zeros, all ones and toggle. These patterns are output on all four channel data

lines simultaneously. Some patterns like custom and sync are affected by the type of interface selected,

serialization and bit order.

Table 25. Test Patterns

PATTERN

DESCRIPTION

All zeros

Outputs logic low.

All ones

Outputs logic high.

Outputs toggle pattern - <D13-D0> alternates between 10101010101010 and

Toggle

01010101010101 every clock cycle.

Outputs a 14-bit custom pattern. The 14-bit custom pattern can be specified into two

Custom

serial interface registers. In the 2-wire interface, each code is sent over the 2 wires

depending on the serialization and bit order.

Sync

Outputs a sync pattern.

Outputs deskew pattern. Either <D13-D0> = 10101010101010 or <D11-D0> =

Deskew

01010101010101 every clock cycle.

Table 26. SYNC Pattern

INTERFACE

SERIALIZATION

SYNC PATTERN ON EACH WIRE

OPTION

14 X

MSB-11111110000000-LSB

1-Wire

16 X

MSB-111111111000000000-LSB

14 X

MSB-1111000-LSB

2-Wire

16 X

MSB-11110000-LSB

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