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Pull-up and Pull-down resistors on ADSP-21479 Custom Board

Question asked by Pradeep on Nov 11, 2010
Latest reply on Nov 11, 2010 by DivyaS

Hi,

 

I am working on a custom board with ADSP-21479 processor and I have read the EE-305 application note, which talks about "Designing and Debugging System with SHARC Processors". It is mentioned that, there is no need to have external pull-up/pull-down resistors on the pins of the processor,  that already have internal pull-up/pull-down resistors. But, when I refer to the ADZS-21479-EZ-LITE schmeatics, I found pull-up/pull-down resistors on the pins that feed external components (eg: flash memory), even though these pins are provided with internal pull-up/pull-down resistors. For example, ADSP-21479 processor DAI and DPI pins have internal resistors, but when they are connected to external memory through SPI interface, they are again provided with external pull-up/pull-down resistors. Another example, TRST pin on the JTAG interface has an internal resistor but is shown to have an external pull-down resistor in the EZ-KIT schematics. Can someone provide me more information on this? (where do I require external resistors on my custom board?)

 

Also, Can I use the EZ-KIT schematics (especially JTAG, SPI, DAI, DPI, XTAL interfaces) as a reference while designing my custom board with the ADSP-21479 processor? Does these schematics require any changes when mapped from EZ-KIT to custom board (planing to use USB-ICE-Emulator)? (Just like mapping the PIN 1 of JTAG interface[connected to Vdd on the EZ-KIT schematic] to GND on the custom board).

 

Thanks & Regards,

Pradeep.

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