CS5378 datasheet(63/88 Pages) CIRRUS

63 / 88 page

CS5378

DS639F2

18. TIME BREAK CONTROLLER

A time break signal is used to mark timing events

that occur during measurement. An external signal

sets a flag in the status byte of an output sample to

mark when the external event occurred.

A rising edge input to the TIMEB pin causes the

TB timing reference flag to be set in the serial data

status byte. When set, the TB flag appears for only

one output sample in the status byte. The TB flag

output can be delayed by programming a sample

delay value into the TIMEBRK digital filter regis-

ter.

18.1 Pin Description

TIMEB - Pin 20

Time break input pin, rising edge triggered.

18.2 Time Break Operation

An externally generated timing reference signal ap-

plied to the TIMEB pin initiates an internal sample

counter. After a number of output samples have

passed, programmed in the TIMEBRK digital filter

of the serial data output word. The TB flag is auto-

matically cleared for subsequent data words, and

appears for only one output sample.

18.3 Time Break Delay

The TIMEBRK register (0x29) sets a sample delay

between a received rising edge on the TIMEB pin

and writing the TB flag into the serial data status

byte.

The programmable sample counter can compensate

for group delay through the digital filters. When the

proper group delay value is programmed into the

TIMEBRK register, the TB flag will be set in the

status byte of the measurement sample taken when

the timing reference signal was received.

18.3.1 Step Input and Group Delay

A simple method to empirically measure the step

response and group delay of a CS5378 measure-

ment channel is to use the time break signal as both

a timing reference input and an analog step input.

When a rising edge is received on the TIMEB pin

with no delay programmed into the TIMEBRK reg-

ister, the TB flag is set in the next serial data status

byte. The same rising edge can act as a step input

to the analog channel, propagating through the dig-

ital filter to appear as a rising edge in the measure-

ment data. By comparing the timing of the TB

status flag output and the rising edge in the mea-

surement data, the measurement channel group de-

lay can be determined.

TIMEB

in Serial Data

Status Byte

Delay Counter

TIMEBRK

TB Flag

Figure 37. Time Break Block Diagram

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