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  1. #21
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    Re: Failing to program ALTERA Max 7000A

    OK so correct me if I'm wrong. Looking at the waveform of FvM and the picture of TAP FSM I can tell that JTAG stays in reset state for the first six 1s of TMS, then goes to idle for one clock cycle, then "select DR scan", "capture DR", "shift DR" and from there it remains in that state. During shift, TCK increases in frequency and also the system does a bunch of shift bit runs, each separated by a small pause from the following one.. maybe to let the system process the received data from the TDO shift out line? So I have read some documentation and I know that the serial input can be sent to different registers. They are grouped in Data and Instruction. The two flows in the fsm state diagram are the same just split in DR and IR. But now I'm a little confused. At this point I expect that JTAG would actually first run a small IR scan to put a specific instruction in the instruction register, so that the following DR scan would use the content of this register to redirect the input and output line to the IDentification registers, because I have read that even among DR type scans there are different possible choices of register, but in the waveform the JTAG seems to go directly for the DR scan.. Maybe in this case ID register is considered as default and there is no need to specify it through the IR? Thanks



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  2. #22
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    Re: Failing to program ALTERA Max 7000A

    The six 1s on TMS will force a JTAG TAP FSM to the reset state from anywhere in the TAP FSM. It's why TRST is optional.

    From power on reset a device is supposed to output it's ID when initially scanned, so no need to specify a command.


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  3. #23
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    Re: Failing to program ALTERA Max 7000A

    I see thanks a lot
    By the way I noticed that trying to understand how does a standard interface work by reading the official technical documentation is an extremely tedious job. Is there some other standard practice to learn in a simpler way? Like I can imagine learning the general functioning in a simple way and only after referring to the technical doc for particular details. Maybe just regular googling or even books?
    For example I remember trying to implement myself the usb1 protocol with Arduino only to give up and use a library because of the tremendous time investment that I estimated by browsing the official documentation



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  4. #24
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    Re: Failing to program ALTERA Max 7000A

    Usually it requires reading the standard, occasionally you might find a tutorial that describes the highlights of the standard. JTAG isn't that hard of a standard to understand, though I've forgotten most of what is in there since I haven't had to design something that is JTAG compliant for 20+ years.



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