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Question & Answer
Classification:
Date: Aug 11, 2000
Problems reprogramming the XSV Board oscillator frequency
Q:
I've been using the XSV board for several months with great success. However, I've been running with an oscillator frequency of 50 Mhz (ie divisor or 2) and now need to change this to 20 Mhz. When I go through the steps in the XSV manual to change the divisor, the speed does not change. I did this successfully when I first got the board (unless 50 Mhz is the default and I just thought it worked), and had assumed I could change it again later. We did make one minor change to the board; we cut resistor R21 which goes to the video codec.
Could you provide any guidance on changing the oscillator frequency?
A:
Here are some items to consider:
- The CPLD is reprogrammed when programming the oscillator. Do you have a shunt on J23 so the CPLD can be reprogrammed?
- Some parallel ports put out enough power through their drivers to keep the XSV Board in a semi-powered state. This can prevent the oscillator from entering programming mode even when you cycle the board power. Try turning off the power and removing the parallel port cable when you remove power to change the J22 and J36 jumpers.
- When the CPLD is configured to program the oscillator, it drives the programming signals into the oscillator output pin. This CPLD configuration can prevent the oscillator output from oscillating if you try to power up the board and oscillator after programming. To remedy this situation, re-run GXSTEST to reprogram the CPLD with a circuit that frees the oscillator output. Then check the oscillator frequency.