MCF51QE128 - CPU speed

[Richard777]

Hi, I'm a MCF51QE128 beginner, I will be select a 16 Mhz Xtal like external oscilator, and I will be select the internal bus frecuency to 24 Mhz, with this values the frecuency of Core is 48 Mhz ?

Thanks in advance

--
Alban Edit: Please always include FSL Part Number in Message Subject line.
http://forums.freescale.com/freescale/board/message?board.id=FORUMUSE&message.id=865

Message Edited by Alban on 2007-10-15 11:57 AM

[UK_CF_FAE]

Hi Richard,

On the MCF51QE128 the instruction clock is the same frequency as the output from the ICS, and the bus clock (peripherals etc) is divided by 2.

Instruction clock = ICSCLK

Bus Clock = ICSCLK / 2

Device Reference Manual, PDF page 24. Figure 1-3

So, yes, if you use the 16MHz crystal, set the FLL to generate 48MHz, then the core will run at 48MHz and the peripherals at 24MHz.

I reckon

ICSC1_CLKS = 00

ICSC1_RDIV =  100

ICSC1_IREFS = 0

ICSC2_RANGE = 1

ICSSC_DRS = 10 (FLL factor is 1536)

This is going to give 48MHz exactly. Good luck

Mark

[Richard777]

Alban sorry for my mistake and Mark a lot of thanks for your explanation

Bye