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16 page 
IMPLEMENTATION NOTES FOR THE UR5HCSPI Copyright Semtech 1997-2001 DOC5-SPI-DS-117 www.semtech.com 16 The following notes pertain to the suggested schematic found on the previous page. The Built-in Oscillator on the UR5HCSPI-06 requires the attachment of the 2.00 MHz Ceramic Resonators with built-in Load Capacitors.. You can use either an AVX, part number PBRC-2.00 BR; or a Murata part number CSTCC2.00MG ceramic resonator. It may also be possible to operate with the 2.00 MHz Crystal, albeit with reduced performance. Due to their high Q, the Crystal oscillator circuits start-up slowly. Since the SPICoderTM constantly switches the clock on and off, it is important that the Ceramic Resonator is used (it starts up much quicker than the Crystal). Resonators are also less expensive than Crystals. Also, if Crystal is attached, two Load Capacitors (33pF to 47pF) should be added, a Capacitor between each side of the Crystal and ground. In both cases, using Ceramic Resonator with built-in Load Capacitors, or Crystal with external Load Capacitors, a feedback Resistor of 1 Meg should be connected between OSCIN and OSCOUT. Troubleshoot the circuit by looking at the Output pin of the Oscillator. If the voltage is half-way between Supply and Ground (while the Oscillator should be running) --- the problem is with the Load Caps / Crystal. If the voltage is all the way at Supply or Ground (while the Oscillator should be running) --- there are shorts on the PCB. Note: When the Oscillator is intentionally turned OFF, the voltage on the Output pin of the Oscillator is High (at the Supply rail). |
