Serial In/Out with ISR

SailerMan

What is the formula for determining the baud rate for the SX48 @ 50MHZ and an ISR of 74 Clocks. Using a baud rate of 9600 and 19200. I have a formula at home that seems to work but I get flaky results.

Regards,
Eric
·

Bean

Eric,
It depends on the oversampling used in the interrupt code. It seems that 3x is the mimimum. So that would be 57600 interrupts per second for 19200, and 28800 interrupt per second for 9600.

The ISR cycles wouldn't make any difference (as long as it finished before the next ISR is due).

Bean.

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Rsadeika

Hopefully, in one of the new books, they will devote, maybe a chapter, that shows how to deal with this problem, at least a problem·for me anyway. Also, lots of examples with maybe working UART program in SX/B that has a functioning Rx and Tx.

The problem that I have is,·as soon as you want to change something like the freq, and the baud rate, everything goes down hill for me.

Ray

JonnyMac

Did you know that in the latest version of SX/B (1.51.03) the INTERRUPT keyword has a rate parameter that lets you specify interrupts per second? With this, all the dirty work is handled and you can change frequency without having to rewrite your interrupt code. That takes care of the freq problem; if you change the baud rate then you may have to touch up the code (perhaps change a constant value).

I'm not to the advanced section of my book yet so I have made a mental note for myself to make sure I have some coverage on this topic.

Post Edited (JonnyMac) : 1/22/2007 11:29:34 PM GMT