topic Re: External bus interface and Pierce oscillator in S12 / MagniV Microcontrollers

External bus interface and Pierce oscillator

Ebda — Wed, 26 Apr 2006 22:04:44 GMT

Hi, i'm using 16 bit microcontroller MC9S12XDT512CAG in normal expanded mode and i selected 25MHz as crystal frequency. I tied the XCLKS\ pin low configured to full swing pierce cyrstal oscillator(0.5 to 40MHz range). I'm interfacing 3.3V lan device with 5V tolerant input to MC through External Bus Interface (PORTS A, B, C, D and E).

1. would this 25 MHz pierce oscillator would works in this configuration.

2. please can any body tell me what is FULL SWING pierce crystal oscillator. and can suggest any manufacturer..?

3. I didn't able find the relation between external bus frequency, system clock frequency. In this case what is the bus frequency?

4. Datasheet MC9S12XDP512V2.pdf page-837 signifies, by setting the ITHRS bit of EBICTL0 register we can configure the EBI to communicate with 3.3V devices with 5v tolerant inputs. But i'm not find the REDUCED INPUT THRESHOULD VOLTAGE LEVELS???? Please any body inform me regarding this.

Please any body help me.......

Awaiting for ur reply.

Ebda

Re: External bus interface and Pierce oscillator

Nabla69 — Thu, 27 Apr 2006 14:56:42 GMT

Hi Ebda,

1. Yes, limit of external bus is 20MHz on S12XDT.

2. I believe full swing means it oscillate between the rail voltages, here 0-2.5V. But I'm not 100% positive.

3. External Bus Freq = Bus Freq, except you can add WAIT states or clock stretches to external. On S12, if not using anything like PLL, the Bus Freq = Osc Freq / 2. Therefore, if the Bus is powered straight from your 25MHz XTAL, you will get a 12.5MHz internal & external bus.

I don't know what a "system clock" is.

Cheers,

Alvin.

Re: External bus interface and Pierce oscillator

Ebda — Fri, 28 Apr 2006 12:12:34 GMT

Hi Alvin,

Thanks for your helpfull reply.

i;m using the microcontroller in Normal expanded mode. i need to varify the timing diagram. i'm in confusing with timing diagram varifycation. tell me what are important things i need to consider in varifying the timing diagrams. is there any example timing diagram for external bus interface with any device. please help me...

Regards

Ebda.

Message Edited by Ebda on 04-28-200612:19 AM

Re: External bus interface and Pierce oscillator

Nabla69 — Fri, 28 Apr 2006 17:51:54 GMT

You're welcome,

For your timing considerations, I would advise you a look at the Application Note AN2708-AnIntroductionToExternalBusonS12X written by Daniel.

The document will show you the impact of clock stretches on the diagram.

Alvin.