[DSP-10] Processor stuck....???

[Jonathon Ayres]

Hello Hermann

 From a look at the spec sheet for the ADSP-2181 and from some past 
experience, your problem could be due to a poor solder joint somewhere on 
your board.

Check all of your connections to R5, the pullup resistor to the /IS input 
(active-low, IDMA Input Select line).  If there is a faulty connection 
present, this could easily request an Internal DMA (IDMA) bus transaction 
to the ADSP-2181's I/O port.  If this were to occur, then the processor 
could then respond to an asserted level on the IAL (Internal DMA Port 
Address Latch Enable).  Since your current remedy is to pull the IAL line 
low, effectively de-asserting it, it makes sense that your IDMA  port is 
being activated somehow.  Since the IDMA port is not used, it should be 
disabled, and I think that is the purpose of the R5 pullup.

It also would be a good idea to check all of your connections to R21, the 
pullup resistor to the /BR input (active-low, bus request input), since 
this pin will initiate a bus request to the ADSP-2181 when it goes low.

Its not surprising that pressure applied to the DSP chip could cause the 
board to stop working, especially if there were a break in the signal path 
to the /IS pin - that was initiated by the pressure on the chip.  Also, 
keep in mind that CMOS inputs typically exhibit very high values of input 
impedance.  I remember on one occaision where I had a floating input to a 
CMOS gate on a board that I was testing.  In this instance, I was able to 
affect the logic level of this input by moving a charged object (plastic 
bottle, for example) to within a foot or so - of the component's 
location.  Apparently, the static field potential was enough to induce a 
charge onto the line that fed the gates input and thus would change the 
logic level into the gate !   This made for some very bizzarre circuit 
behavior and had me running around a bit until I figured out what was 
happening.

Anyway, good luck with it - and I hope this helps !

Jonathon Ayres


At 12:04 PM 3/21/02 -0500, you wrote:
>Hi All....maybe sombody has the same problem... (maybe it isnt a actual
>problem?)
>
>EZ Kit in the Box, well shielded...but as soon as I put my fingers at the
>processors-top (insulated..not touching any pin !) the time-ticks go off  and
>after I take my fingers away it takes some time and normal oparation is
>resumed. Sometimes it screws up the whole program and I have to reset and
>reload both programs.
>
>Friend Walter found out that this has to do with PIN 20 on P3:2, which leads
>to PIN 125 (the last PIN on the "Zero" corner) on the ADSP 2181 and it is an
>input Signal called  I A L .  So far I can see, this signal is not used in
>our application. If this PIN gets grounded by a 100 K resistor, everything is
>fine.
>
>Could this cause problems and who got the same experience ???
>
>Answers wellcome,,,,, de DC9UP Hermann
>
>
>
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