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The article that I linked to talks about the micro and SPI slave (on CPLD) possibly going out of sync when only the clock and data lines are used. When the micro starts up it could put a clock pulse on the SPI slave and the SPI slave will then clock in one bit. When the real data byte is sent...
Yes, try that...
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Just to clear that up, you must have the when others=> part or you will get an error. Don't use null in it or you will make a latch.
If you want to be able to detect the PWM input clock edges, then use a pin that has "interrupt-on-change" capabilities (only available on PORT B I think)
The VHDL code for the SPI slave is even simpler if you use the slave select pin from the SPI master instead of trying to count the clock pulses. **broken link removed** contains two VHDL examples.
Do you want to make a single tone that is a continuous 2kHz?
I built a wailing siren circuit, but it uses two 555 timers. The tone changes up and down. You can find it at this website:
**broken link removed**
Are you wanting to use one 555 timer?
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