crystals powering multiple devices (bit-bang simulation of SPI)

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In general you CAN use a crystal to clock (not power) more than one device. You use the xtal controlled oscillator of device one and take a clock output from device one to drive the clock input of device two. If there is not a clock output or input, you may with caution, take the driven terminal of the xtal on device one as the clock output and connect it to the xtal input of device two. It may require some series resistance to limit the drive level. Do not connect the xtal drive pin of device two. For parallel mode crystals, the shunt capacitors should be reduced in value to reduce crystal loading by the added circuitry. In some cases, buffering may be required depending on the specific circuit.

Another option is to use a ready made xtal oscillator instead of an xtal and connect it's output to the two clock or xtal inputs on the two devices. A

555 is not a suitable device for an xtal oscillator or buffer. However, you can make oscillators and buffers with CMOS inverters. Bob

Yes, it's possible to use one crystal to clock multiple devices provided that the clock signal is suitably 'strong' or adequately buffered.

555s don't use crystals though. They are RC based timers.

You may want to look at this Intel application note. It's very useful.

Graham

Hi Group,

Thank you for all the help with my question earlier about UART to SPI, this is a follow up question...

Can the same crystal be used to power 2 different devices? Is there any danger in using that?

The current situation is, I have a UART which support bit-bang simulation (FTDI232BM), but the problem is that I don't know how to generate the Clock signal, since the FTDI232BM bit-bang creates 8 GPIO lines for this, but I'm thinking that software generated CLK signals will be highly unstable?

Since the timing signals of the FTDI232BM is not exported, I'm thinking that if I also use the crystal to power a 555 timer, and then I will have a signal at the correct frequency (and also a signal equivalent to the one being generated in the FTDI232BM during sending of data?)

Thanks in advance

Kelvin