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comments on doc/manual/primer/jtag.txt 

1. fix some errors in jtag.txt(in my personal opinion, please review).
2. remove a broken link

Signed-off-by: Jun Ma <sync.jma@gmail.com>
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>
__archive__
Jun Ma 2010-05-14 21:43:11 +08:00 committed by Øyvind Harboe
parent 9597dcefaa
commit b8c54b362b
1 changed files with 6 additions and 10 deletions
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doc/manual/primer/jtag.txt
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@ -29,7 +29,7 @@ TMS which will select different shift registers.
The first thing you need to do is reset the state machine, because when The first thing you need to do is reset the state machine, because when
you connect to a chip you do not know what state the controller is in,you need you connect to a chip you do not know what state the controller is in,you need
to clock TMS as 1, at least 7 times. This will put you into "Test Logic to clock TMS as 1, at least 5 times. This will put you into "Test Logic
Reset" State. Knowing this, you can, once reset, then track what each Reset" State. Knowing this, you can, once reset, then track what each
transition on TMS will do, and hence know what state the JTAG state transition on TMS will do, and hence know what state the JTAG state
machine is in. machine is in.
@ -45,9 +45,9 @@ instruction register.
For example, one of the data registers will be known as "bypass" this is For example, one of the data registers will be known as "bypass" this is
(usually) a single bit which has no function and is used to bypass the (usually) a single bit which has no function and is used to bypass the
chip. Assume we have 3 identical chips, wired up like the picture chip. Assume we have 3 identical chips, wired up like the picture(wikipedia)
and each has a 3 bit instruction register, and there are 2 known and each has a 3 bits instruction register, and there are 2 known
instructions (110 = bypass, 010 = some other function) if we want to use instructions (110 = bypass, 010 = "some other function") if we want to use
"some other function", on the second chip in the line, and not change "some other function", on the second chip in the line, and not change
the other chips we would do the following transitions. the other chips we would do the following transitions.
@ -66,13 +66,13 @@ each chip [110] [010] [110]
The order is reversed, because we shift out the least significant bit The order is reversed, because we shift out the least significant bit
first. Then we transition TMS: first. Then we transition TMS:
1 1 1 1 0 0 1 1 1 0 0
which puts us in the "Shift DR state". which puts us in the "Shift DR state".
Now when we clock data onto TDI (again while holding TMS to 0) , the Now when we clock data onto TDI (again while holding TMS to 0) , the
data shifts through the data registers, and because of the instruction data shifts through the data registers, and because of the instruction
registers we selected (some other function has 8 bits in its data registers we selected ("some other function" has 8 bits in its data
register), our total data register in the chain looks like this: register), our total data register in the chain looks like this:
0 00000000 0 0 00000000 0
@ -107,10 +107,6 @@ gets interesting. But in and of itself, JTAG is actually very simple.
@section primerjtag More Reading @section primerjtag More Reading
The following link goes to an HTML (or PDF) introduction to JTAG,
written by one of the original members of the JTAG committee: @par
http://www.asset-intertech.com/products/boundscan.htm
A separate primer contains information about @subpage primerjtagbs for A separate primer contains information about @subpage primerjtagbs for
developers that want to extend OpenOCD for such purposes. developers that want to extend OpenOCD for such purposes.