RE: Re: Question about IMB

1. Yes, the MPC555 operates at a system clock speed up to 40MHz.  You have to program the PLPRCR register (MF) to get desired frequency.  The CLKOUT pin will generally reflect the system clock frequency and is the easiest way to check if you are unsure.

2. The default (i.e. out of reset) IMB frequency is half the system clock frequency.  You can program it to full frequency as follows:
	UIMB.UMCR.B.HSPEED = 0;

Regards,
Allan

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of lmdinnin
Sent: Wednesday, April 20, 2005 9:36 AM
To: [email protected]
Subject: [MPC500] Re: Question about IMB




I was just about to make a post, but the search feature is a 
wonderful tool!

Anyhow, I'm currently configuring the TPU on my MPC555 (Phytec Dev. 
Board) to do some input capturing.  I got lost in the technical data 
regarding the clocks, specifically:

1. The MPC555 product brief says it (the MPC555) operates at 40MHz.  
Does this mean that the system clock frequency is 40MHz?

2. Depending on the answer to #1, what is the default IMB speed?  I 
say default because I am trying to do all my programming using 
Matlab's Real-Time Workshop, and I don't know how to (hopefully, 
don't need to) change the IMB speed (as it relates to the system 
clock) from Matlab.  I see from your reply below, Randy, that 
IMB "can" run at the system clock frequency, but assuming I am just 
turning the thing on and downloading a Simulink program, what speed 
does it run at?

...from there, the MPC555 Embedded Coder's Resource Configuration 
Block makes the prescaling/scaling of TCR1 easy.

Thanks for the help, I hope I provided enough info.

Regards,
Liam


--- In [email protected], Dees Randy-rsaf30 <randy.dees@f...> 
wrote:
> the IMB can run at the same frequency as the system clock (up to
the maximum frequency rating of the device which is either 40, 56, 
or 66 MHz).
>  
> the TPU runs on the same frequency as the IMB, but fastest the
TCR1 clock can run is system frequency divided by 2 - see the EPSCLK 
settings..
>  
> randy
> 
> -----Original Message-----
> From: James Smith [mailto:jasmith@c...]
> 
> 
> Hi folks,
> 
> I'm trying to figure out how fast the TPU  on the '565 can go,
which I  
> understand is related to the frequency of the IMB.  In the
MPC565 "Fact  
> Sheet"
> (http://e-www.motorola.com/files/microcontrollers/doc/fact_sheet/ 
<http://e-www.motorola.com/files/microcontrollers/doc/fact_sheet/>  
> MPC565FACT.PDF) it states that the TPU operates at half the
system  
> speed (so at a max of 28MHz if the 565 is running at 56 MHz).  But
in  
> AN1778
> (http://www.freescale.com/files/microcontrollers/doc/app_note/ 
<http://www.freescale.com/files/microcontrollers/doc/app_note/>  
> AN1778.pdf) it seems that the IMB (at least on the 555) can be set
to  
> the full system speed ("Normally, the IMB (intermodule bus) clock
is  
> half the system clock, but for this example it has to be set to
full  
> speed at 20 MHz in the initialization script. This was done to
maintain  
> consistency if the system clock is set to 40 MHz with a default
half  
> speed bus of 20 MHz. The IMB can be set to 20 MHz whether the
MPC555 is  
> operating at 20 or 40 MHz.").
> 
> So could I run the IMB (and therefore the TPU) on the 565 at the
full  
> 56 MHz?  If so, is there anything wrong with doing this?  For
instance,  
> would it drop edge counts during quadrature decoding or something
like  
> that?
> 
> 
> 
> [Non-text portions of this message have been removed]



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