ColdFire/68K Microcontrollers and ProcessorsのトピックM5221X Bus Frequency

M5221X Bus Frequency

mjbcswitzerland — Fri, 11 Jul 2008 05:12:12 GMT

Hi All

I am a little confused as to the maximum bus frequency quoted on the M5221X Product Summary Page:
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MCF5221X&nodeId=0162468rH3YTLC00M95448&tab=Buy_Parametric_Tab&fromSearch=false

The M5221X types are given to have 25MHz to 40MHz maximum bus speed.
In the data sheets and user manual the values of 50MHz to 80MHz are specified.

[As a comparison - the M5222X are specified on the product summary page to have max. bus speed of 80MHz, corresponding to the same value of 80MHz as specified in the data sheet].

Is this an error or a different interpretation?

Regards

Mark

www.uTasker.com

Re: M5221X Bus Frequency

RichTestardi — Fri, 11 Jul 2008 06:12:26 GMT

Hi Mark,

Isn't the CPU speed twice the (I/O) bus speed? Or did I misunderstand totally? All the peripherals seem to operate that way?

-- Rich

Re: M5221X Bus Frequency

JimDon — Fri, 11 Jul 2008 06:16:20 GMT

Mark,
Yes, I did notice that. I think the various docs use incorrect terminology. The max. clock rate is 80Mhz, which should be called the System clock, and the (IO) bus clock is system clock/2. So that would mean that the (IO) bus clock is 40 MHz max. At different points they seem to confuse these terms, and possible introduce other terms. The seem to use "bus clock" to refer to both the CPU (System) bus and the IO bus clock.

Re: M5221X Bus Frequency

SimonMarsden_de — Mon, 14 Jul 2008 16:18:34 GMT

Yes, be careful. This problem affects much of the ColdFire documentation.

You need to treat the term 'System Clock' with caution in any ColdFire manual. It is sometimes used for the bus clock and sometimes for the core clock.

In some of the manuals there is a helpful diagram (usually in the PLL section), which shows the clock routing to all the peripherals. You can use it to check which ones receive a divided-by-two bus clock.