operating NE64 at 50 MHz in expanded bus mode

[Danish]

Hi,

 I am using MC9S12NE64. We have got external RAM  in our design to store data and an extrernal crystal clock of 25MHz.

 I want to know what is the maximum frequency we can operate NE64 processor,  when using expanded mode operation.

Processor datasheet says that operating frequency is 32 MHz in expanded bus mode and 50MHz for single chip mode.

 Can I run the processor at 50MHz while being in expanded bus mode ? Is it allowed?

What impact this might have on the processor?

- Dan

[Danish]

Thanks.

Is it possible to execute the code in expanded mode and run at 25MHz without accessing external memory. (Memory is connected but not used)?

I want to execute the code at 25 MHz for faster processing, but while accessing external RAM (read/write), i can scale down the speed to 16 MHz (through PLL).

Any thoughts on this.

[samiran_cj]

Accidently overclocking would probably fry the chip. I2C or SPI bus for external storage might help you instead. You could then run at the maximum speed.

[mjbcswitzerland]

Hi

With some tricks many things are possible, but don't forget that there will be a delay when changing the PLL until it has locked again. I don't understand which times will be relevent from the data sheet but expect it to be 0,5ms or so. This will probably mean that the code will have to wait when switching and this may cancel any advantages.

The Ethernet will still not operate at 100M because it would run out of specification whenever the speed was increased. There are a few setting which have to match the bus speed (Ethernet settings and flash times spring to mind) and so it would be necessary to make sure that these are also in synch with the present setting - assuming that they can be programmed more than once [some registers can only be written once]

Personally I would not attempt manipulating the PLL/external bus use but who knows, it may work for you (?).

Regards

Mark Butchjer
www.mjbc.ch

[EMontanez]

_sam_ is correct! In expanded modes the NE64 can only run at a maximum 16MHz bus clock.

Message Edited by EMontanez on 03-20-2006 11:37 AM

[mjbcswitzerland]

Hi

Note that there is a restriction when operating with a bus speed limited to 16MHz: since the Ethernet interface required 25MHz bus to operate at 100M, it will only be able to work at 10M. This is maybe the biggest restriction when using expanded modes....

Regards

Mark Butcher

www.mjbc.ch

[samiran_cj]

"User should note that the NE64 device has a 16Mhz rated external bus capability and that 25Mhz operation should not be expected in NE64 product designs."

As far as I understood from this documentation you are not recommended to run the external bus at more than 16MHz when you use it. You will then have to scale the (internal) Bus Clock down from 25 to 16 MHz to use the RAM on the external bus.

Hope this helps...