MCP3903 ADC Evaluation Board for 16-Bit MCUs User’s Guide
DS51994A-page 8
©
2011 Microchip Technology Inc.
1.2.1
Using the Crystal X2
The MCP3903 ADC Evaluation Board for 16-Bit MCUs is populated with a 3.58 MHz
crystal, being used as a clock source, by placing jumpers in the following position on
the MCP3903 Digital I/O header block:
FIGURE 1-3:
ADC Clock Selection Jumpers - External Crystal.
1.2.2
Driving the Clock with the PIM Module
The PIC
®
MCU can be used to generate the CLKIN (MCLK) signal for the MCP3903,
setting the ADC sample rate through the use of the output compare module OC1. To
use this, make the following jumper change to the MCP3903 Digital I/O header block:
FIGURE 1-4:
ADC Clock Selection Jumpers - Clock from MCU.
The signal frequency from OC1 can be changed by the user from the PC software by
changing the value in the
Sampling Speed Control
box from the
Edit
menu. A low
number will generate a high frequency signal. The value of the sampling rate, which is
directly proportional to the clock frequency from OC1, is indicated in the sampling
speed indicator box in the PC software (see Figure 2-3) for the dsPIC33 example. In
the PIC24F example, the sampling speed is constant at 4.8 ksps, regardless of the
OSR value.
XTAL
XTAL
PIM OC1
CLKIN
CLKIN
CLKOUT
XTAL
XTAL
PIM OC1
CLKIN
CLKIN
CLKOUT
