Hendrik Lipka has written up documentation on his SPG8640-based crystal frequency generator:
When I needed a small frequency generator for a project several years ago, I did neither had the time nor the skills to build something like that. But I had in my parts box a nice chip that seemed perfect for a small tool – the SPG8640BN.
This small chip is a crystal osciallator combined with a configurable divider. The specific ‘BN’ version has a 1MHz oscillator, one divider up to 1:12 and one divider up to 1:107sup>. So it can generate an output from 1/120th up to 1MHz. Nice. Configuration of the output frequency happens via several control pins. The first three select the base frequency, as the control the 1:12 divider. The selectable dividers as 1, 2, 3, 4, 5, 6, 10 and 12. The other three control pins control the second divider, and select the division stage – with each stage dividing by 10. So we have 8 different base frequencies, and each can span 8 decades.
Project info at Hendrik’s blog.