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Part Number: SN74LVT8996
When I scan all the TAPs on my JTAG Bus, one of them answeres with " I-S-10xZERO-S-I "
So far I know, this is the code for a Reset of the device. What can be the reason to induce the SN74LVT8996 to answer with this code instead of its address?
Green SDI (of the BusMaster)
... on my oscilloscope picture...
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In reply to Steffen Jahr:
In reply to Wade Vonbergen:
Unfortunately I have no better zoomed picture in the moment. This one shows the start of the communication. Do you need a better picture? The master changes data and clock separately. The slave sends the Data with the Clock edge.
On our Bus system with a double sided, 21 Position Backplane the problem occured at the Card in the middle of the Bus direct opposite of the JTAG bus master.
On the Backplane are Bus termination resistors, on both ends of the Backplane 220 Ohm against P3.3V, 1 kOhm against GND, resulting in 110 and 500 Ohm.
I measured reflections on the TCK slopes (on the other signals, too)
In the middle of the Bus signal reflections from both sides added in a unfortunately manner and the Logic levels have been reached, I think.
So the one JTAG Bus slave received more clock impulses.
Withe the capacity of the Oscilloscope probe the slopes bekame somehow flatter and the effect has gone...
Thank you for your support!
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