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Voyager
Voyager
360 Views
Registered: ‎05-30-2018

Readback Command Sequence in UG470: typo or error

Hello,

In UG470 at p. 135...137  we can find the sequence dedicated to read configuration memory.

Here is screenshot of p. 136

UG470_Readback_Command_Sequence.jpg

The first part of step 5 (inside red frame) moves TAP state machine to RTI state and remains there for 12 TCK cycles.

According to my calculations TAP state machine won't go to RTI state: given that before execution of the "red frame" sequence, the TAP state machine is in the state Exit1-IR, applying 12 pulses TCK and keeping TMS to '0' will jam the state machine in the state Pause-IR, isn't it ?

Any comments.

Tanks.

P.S. Diagramme of TAP state machine

JTAG_state_machine.JPG

 

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2 Replies
Xilinx Employee
Xilinx Employee
290 Views
Registered: ‎03-07-2018

Re: Readback Command Sequence in UG470: typo or error

Hi @pavel_47

I have checked Virtex-5, Virtex-6, 7-series and Ultrascale configuration guides; I do not see any change in state "Move into the RTI state; remain there for 12 TCK cycle" after state "Shift the MSB of the JSHUTDOWN instruction while exiting SHIFT-IR".

Regards,
Bhushan

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Voyager
Voyager
265 Views
Registered: ‎05-30-2018

Re: Readback Command Sequence in UG470: typo or error

Hello Bhushan,

Thanks for feedback.

I have checked Virtex-5, Virtex-6, 7-series and Ultrascale configuration guides; I do not see any change in state "Move into the RTI state; remain there for 12 TCK cycle" after state "Shift the MSB of the JSHUTDOWN instruction while exiting SHIFT-IR".

Probably each of these documents contain errors. Did you check this sequence on whatever board ?

If we have a look at TAP diagramme, we can figure out that the step 4 is executed as follows:

  • The first 5 bits of JSHUTDOWN instruction are shifted when the TAP state machine is in the state SHIFT-IR
  • When the last bit of the JSHUTDOWN instruction is shifted, the TAP state machine moves into EXIT1-IR state
  • So, before applying 12 TCK cycles, the TAP state machine is in EXIT1-IR state, isn't it ?
  • If you agree with my at this point, I affirme that applying of 12 TCK when is TAP state machine is in EXIT1-IR state and TMS = 0 will drive state machine in PAUSE-IR state (not in RTI state as UG470 affirms !!!)

Sincerely,

Pavel

 

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