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5.2
Digital Control
5.3
Clock Source
EVM Operation
The digital control signals can be applied directly to J2 (top or bottom side). The modular
ADS1241MEVM can also be connected directly to a DSP or microcontroller interface board,
such as the HPA449. For a current list of compatible interface and/or accessory boards for the
EVM or the ADS1241, see the relevant product folder on the TI web site.
5.3.1
Onboard Oscillator
The ADS1241 requires a clock. A 4.9152MHz crystal is provided on the EVM, and may be
selected as the clock source for the device when switch S8 is in the right-hand position.
5.3.1.1 Oscillator Kickstart (Experimental)
Because the ADS1241 is a low power device, its clock oscillator circuit does not have extremely
strong drive capabilities. Using the crystal and load capacitor values provided on the EVM, the
clock oscillator starts up and works reliably. However, some users may wish to try a different
crystal or load capacitor values, and in some cases the ADS1241 clock oscillator will take a long
time to start up.
To help decrease startup time, the circuit built around U5 is provided on the EVM. This is only
for experimental purposes and has not been proven nor is it recommended; it is provided only as
a possibility for decreasing oscillator startup times. This
kickstart
circuit is designed to provide a
pulse of energy to the crystal to help get it started oscillating.
In use, the enable for the kickstart circuit (GPIO2) would be pulled high to activate the circuit. A
rising edge would then be applied to GPIO1, which should result in a pulse appearing at the
output of C19. Once the crystal has begun oscillating, GPIO2 should be brought low to remove
the kickstart circuit from the oscillator.
5.3.2
External Oscillator
When S8 is switched to the left, the clock source for the ADS1241 is provided from J2.13.
ADS1241MEVM
6
SBAU106–October 2004