Zongo
Joined: 24 Apr 2004
Posts: 1
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 24 Apr 2004 5:02 ADSP-2191 : hardware design trouble |
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Hi, all !
I'm sure we have all faced this situation once : we have a simple idea, using a great-looking part, and as soon as we want to design a prototype board... ALL HELL BREAKS LOOSE 
I'm in the process of designing a simple board for the purpose of evaluating the ADSP-2191 in a very specific context. So specific in fact, that I don't need any of the following :
- No Host Port Interface
- No Sports
But I do need the programmable flags PF0..PF7 , although they might end up unused sometimes.
Here's the thing that gets me worried : what do I do with all the unused pins ?
The inputs I can manage, but some pins are marked as I/O/T and it isn't clear what is there status at reset : I, O or T ?
Also, I'm having trouble with the PLL : the EE-153 note from AD states that if you use BYPASS then the flags are still scanned on reset but aren't used to set the frequency ratio (which you can then modify in software).
However, (maybe I'm blind) I couldn't find in the datasheet the default status of the flags : I ? O ? T ?
Assuming I set the PLL in bypass mode, can I leave PF0..7 floatting ? Or do they default as input anyway and require a pull-up ?
Close examination of the schematics of the 2191 EZ-KIT board hasn't been any helpful : the guys at AD have put pull ups on EVERYTHING, including /BMS and every memory strobe, even though they are OUTPUTS and are used.
I've got nothing against being careful, but come on ! They even placed two pull ups on each programmable flag ! Plus a third one that is activated on reset to set the clock ratio !
I'm starting to pull my hair out... help me please : all I want to do is to connect together :
- One ADSP-2191
- One DSM-2150F5V (ST Micro, a FLASH + PLD device with JTAG ISP dedicated to booting ADSP's)
Assume I want to leave every other pins (PFx, SPORT's, Host Interface) unused.
I'll add that I'm not the only engineer facing this problem.
If this keeps up, I'll just go crazy and put pull-up resistors on everything that moves, including the ground pins, the clock input, Vddint, my girlfriend and the neighbor's car. I have a soldering iron and plenty of 0603 ammunition... err I mean resistors 
Jean (not desperate... yet  )
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