AFE4400_15 Datasheet, PDF (28/87 Pages) Texas Instruments – AFE4400 Integrated Analog Front-End for Heart Rate Monitors and Low-Cost Pulse Oximeters

AFE4400
SBAS601H – DECEMBER 2012 – REVISED JULY 2014
www.ti.com
8.3.2 Clocking and Timing Signal Generation
The crystal oscillator generates a master clock signal using an external crystal. In the default mode, a divide-by-2
block converts the 8-MHz clock to 4 MHz, which is used by the AFE to operate the timer modules, ADC, and
diagnostics. The 4-MHz clock is buffered and output from the AFE in order to clock an external microcontroller.
The clocking functionality is shown in Figure 38.
Timer
Module
Divide-
by-2
ADC
Oscillator
Diagnostics
Module
XIN
XOUT
8-MHz Crystal
CLKOUT
4 MHz
Figure 38. AFE Clocking
8.3.3 Timer Module
See Figure 39 for a timing diagram detailing the various timing edges that are programmable using the timer
module. The rising and falling edge positions of 11 signals can be controlled. The module uses a single 16-bit
counter (running off of the 4-MHz clock) to set the time-base.
All timing signals are set with reference to the pulse repetition period (PRP). Therefore, a dedicated compare
register compares the 16-bit counter value with the reference value specified in the PRF register. Every time that
the 16-bit counter value is equal to the reference value in the PRF register, the counter is reset to 0.
28
Submit Documentation Feedback
Product Folder Links: AFE4400
Copyright © 2012–2014, Texas Instruments Incorporated