Przemyslaw Iskra

ColdFire V2 - electrical guide ?

Discussion created by Przemyslaw Iskra on Mar 20, 2009
Latest reply on Mar 21, 2009 by Mark Butcher

Hello.

 

I'm building an input-output board based on MCF52259CAG80 (that's the 144 LQFP one). You may find some information about it here: http://labserver.uv.es/ioboard/ .

 

I'm still not sure how to setup the clocking. I want working USB (as device only), MCU clocked near its maximum frequency and possibility to use UARTs at standard RS-232 frequencies. My guess it that there is no other way than to connect 48MHz source to USB_ALTCLK, use some crystal multiple of RS freqs and multiply it with PLL to drive internal clock near 80MHz. But I don't like the idea of designated USB clock while I could just connect the XTAL directly. Clocking UARTs from timer inputs isn't really interesting either, because I won't be able to divide that frequency.

 

My other concern are the connections through resistors. M52259EVB uses resistors on almost all the signals, to reduce EMI as it says. Should I really take EMI into account ? On the other hand, M52259DEMOKIT uses resistors on clock pins only, probably to make sure no clock edge is detected while not all the signals are ready, but I couldn't find any information about it. Is my reasoning right? That's where a decent electrical guide would be helpful.

 

Thanks, in advice, for any usefull response.

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