Crystal oscillator question

Hallicks

In my report, I'm trying to justify the use of the propeller chip where I could have used a different micro that was suitable for one thing (sync counting) but not another (video generation). Is it to do with the speed of the oscillator, or the processor, or something else?

Mike Green

I can't quite tell what you're asking. If you're asking why the Propeller can generate video and other processors might not be able to:

1) Both the SX and the Propeller can generate video. The SX is somewhat limited in that it can produce only a limited amount of text on the screen while the Propeller can produce standard video in both text and graphics up to the limitations of the media (NTSC or PAL) or VGA text and graphics limited mostly by the amount of internal memory. It will mix some graphics with nice text easily up to 1024x768 and can demonstrate text output to 1600x1200 (without being able to do much else).

2) Both the SX and Propeller can do this because their system clocks can go quite high. The SX can be clocked up to 75MHz (75MIPS) while the Propeller can go up to 80MHz (20MIPS). The Propeller can do more partly because its instructions and data are 32-bit and it has a more powerful instruction set than the SX. It also has 8 independent processors, each with some local memory and counter/timers and each with a simple video generator (for a total of 160MIPS). For the 1024x768 VGA output, two processors are used for the video driver while one is used for the "main program".

3) Both the SX and Propeller have deterministic instruction sets which allow accurate, reproducible timing of outputs and other external events. In the case of the Propeller, this timing has a granularity of 12.5ns.