Cirrus Logic CS5378 - Manual (Page 63)

CS5378
DS639F3 63
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
register (0x29), the TB flag is set in the status byte
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