topic Is CPU08 address bus frequency 8MHz? in 8-bit Microcontrollers

Is CPU08 address bus frequency 8MHz?

admin — Wed, 02 Jan 2008 17:31:29 GMT

Hi,

In the datasheeto of CPU08, it's said that one of the CPU08 features is 8-MHz CPU standard bus frequency. What's the meaning of this "standard bus frequency", is it the internal address bus frequency or the internal data bus frequency?

Thanks,

Simon

Re: Is CPU08 address bus frequency 8MHz?

bigmac — Thu, 03 Jan 2008 08:27:14 GMT

Hello Simon,

This means that the maximum allowable internal bus frequency has been "standardised" to 8MHz over all HC908 devices. (This limit is not applicable to the newer 9S08 devices.)

The internal bus frequency determines the CPU cycle period, that determines the execution period required for each section of code. For devices that do not contain or use a PLL module, the frequency of the internal oscillator, external clock, or external crystal will usually be four times the internal bus frequency.

Regards,

Mac

Re: Is CPU08 address bus frequency 8MHz?

admin — Fri, 04 Jan 2008 17:08:12 GMT

Hi Mac,

Thanks for your help.

Anohter question, is there any other document except "CPU08 Reference Manual" which can gives more details about the principle of the CPU08? In the "CPU08 Reference Manual" (CPU08RM.pdf), there is a section "Internal Timing" to explain the CPU08 internal timing detail, but it doesn't provide enough details such as why the CPU08 derive its timing from a 4-phase clock, where this 4-phase clock comes from?

Thanks,

Simon

Re: Is CPU08 address bus frequency 8MHz?

eckhard — Fri, 04 Jan 2008 18:06:05 GMT

Hello,

there is an Application Note AN2627 that gives more details about the internal Timing.

http://www.freescale.com/files/microcontrollers/doc/app_note/AN2627.pdf?WT_TYPE=Application%20Notes&WT_VENDOR=FREESCALE&WT_FILE_FORMAT=pdf&WT_ASSET=Documentation

Eckhard

Re: Is CPU08 address bus frequency 8MHz?

admin — Mon, 07 Jan 2008 14:49:34 GMT

Hi Eckhard,

Thanks.

Regards,

Simon