115200 baud works with faster system clock speed?

bill190

I've noticed that if I use the following system clock settings (using object FullDuplexSerialPlus.spin, Parallax Serial Terminal, Parallax USB to serial, and 5MHz crystal), that I will get "gobbledygook" on the terminal at baud rate 115200.

But·the following·will work fine at baud rate 57600...

· _xinfreq = 5_000_000····················
· _clkmode = xtal1 + pll1x

If I use these system clock speed settings or faster...

· _xinfreq = 5_000_000····················
· _clkmode = xtal1 + pll2x

...it will work fine at 115200.

Are there certain clock speeds I should use for faster baud rates?
·

Bean

Faster baud rates will require a faster clock speed.

From your description it looks like the clock must be about 80 times faster than the baud rate.

Bean

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kuroneko

It's just plain numbers, at 115200 baud you have clkfreq/115200 cycles to send out a bit. At 5MHz that's 43 cycles or effectively 10 instructions, NG. The FDS object interleaves TX and RX code (ping-pong multitasking). Sending a bit requires at least 13 instructions plus the time spent in the receiver code. Go figure!