S12 / MagniV MicrocontrollersのトピックTimer

Timer

ernestsnaith — Tue, 02 May 2006 22:19:11 GMT

Just playing with timers and they seem increment every two clock cylces, is this right, i thought it was every 4 or maybe 1.

Re: Timer

imajeff — Wed, 03 May 2006 00:15:08 GMT

Perhaps you could be more specific if you want to know why. There are registers which control how many bus cycles per increment of TCNT. You could also specify what MCU

Re: Timer

ernestsnaith — Wed, 03 May 2006 03:06:54 GMT

Sorry, its a 9s12xdt512, using low power pierce oscillator at 4MHz. I have set the prescaler to the 128 max and set an LED to flash when the timer is over 0xF000. I was curious to see if i understood the timer so i timed how long the LED cycle took, it turned out to be 4.2 seconds. I thought it should be 1/ 4,000,000(clock) / 65536 (max timer value) all * 128 = 2.1 second

Message Edited by ernestsnaith on 05-02-200603:10 PM

Re: Timer

Steve — Wed, 03 May 2006 03:19:24 GMT

If you have a 4MHz crystal the bus speed (and source of the timer clock) is 2MHz so your maths is correct. If you need the S12X to go faster you should enable the PLL.
You can have a larger prescaler on the timer by using the precision mode (see this thread: http://forums.freescale.com/freescale/board/message?board.id=16BITCOMM&message.id=861)

(Alban created link)

Message Edited by Alban on 05-03-2006 11:10 AM