revise my design please!

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revise my design please!

Contributor I

Hi everybody,


My name is François and I am new to freescale controllers. I already played a bit with my Softec starter kit but now I would like to do my owm design.


I have experience with PIC microcontroller and I had a course on "HCS12" but we used a development board and learnt only software design.


I use Altium designer to design my boards

I Would like to use S12XDP512 for different reasons


for now, I have no specific application, I just want to get the controller working on a board I have designed.


I made a small design in altium designer and I would like to have advices from professionals who have more experience than me with these controllers before going too far in design and do something that don't work.


I followed the pcb recommendations on the datasheet and I wonder if these recommendations are overkill or if this is not done properly, the controller just won't work.


I also based my design on the schematics from a development kit.


Here is my circuit design.
























































 My pcb design looks like this






















































Sorry for the size of the pictures... see the copies in attachments


So please fells free to give me any advices about my design, would this work ? could it be better or simpler ?


Thank you very much


I attach my Altium project and library if you want to take a closer look.



Message Edited by t.dowe on 2009-10-20 11:37 PM
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Specialist I

Circuit is almost OK.

How do you power your board? I see no dedicated power connector and BDM pods by default should not power target boards. BDM connector pin 6 usually is used as a reference for BKGD and /RESET levels shifting circuit.

/XCLKS pin is not connected. By default it is pulled high, which means oscilator should work in loop controlled Pierce mode. If so, then R4 should be not installed. But even if crystal oscilator doesn't work, oscilator should keep working in self clock mode and your BDM pod should detect your chip.

Datasheet tells that MODA ande MODB are pulled low at reset, selecting single chip mode, but I would install my own pull resistors on all critical pins, MODA, MODB, /XCLKS. Also on /XIRQ, because even if XIRQ interrupt is disabled, XIRQ pulled low will wake up chip from low power modes.

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Contributor I

Thank you very much,


actually, there is still no power and ground for the board (it is still not a board, more a reference design) I will power the board externally. Where to you usually attach a ground and a 5V trace ? i would use the big red polygon plane at the right for 5V and the middle of the ground star for ground, would this be correct ?


I will add my own pull resistors for MODA, MODB,/XCLKSand on /XIRQ


also I think I will remove R4


I will read the datasheet more about these pins and I will correct my design.



also, I was planning to make the OSBDM to use as a BDM pod, I read that it should work for this controller but I just want to be sure. (will it support programming and debugging the xgate also ?)


also, you said no comments on the pcb design, does it mean it's OK or maybe I can change the layout a bit ? I don't really like the 5V distribution all around the chip I think it makes harder to route the other pins...


thank you for your comments !

Message Edited by Rotule on 2009-05-06 12:40 PM
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