Maxim Integrated 16-6
MAX31782 User’s Guide
Revision 0; 8/11
16.3 Communication via TAP
The TAP controller is in Test-Logic-Reset state after a power-on reset. During this initial state, the instruction register
contains the Bypass instruction and the serial path defined between the TDI and TDO pins for the Shift-DR state is the
1-bit bypass register. All TAP signals (TCK, TMS, TDI, and TDO) default to being weakly pulled high internally on any
reset. The TAP controller remains in the Test-Logic-Reset state as long as TMS is held high. The TCK and TMS signals
can be manipulated by the host to transition to other TAP states. The TAP controller remains in a given state whenever
TCK is held low.
For the host to establish a specific data communication link, a private instruction must be loaded into the IR[2:0] regis-
ter. Once the instruction is latched in the instruction parallel buffer at the Update-IR state, it is recognized by the TAP
controller and the communication channel is established. In-circuit debug or in-system programming commands and
data can be exchanged between the host and the MAX31782 by operating in the data register portion of the state
sequence (i.e., DR-Scan). The TAP retains the private instruction that was loaded into IR[2:0] until a new instruction is
shifted in, or until the TAP controller returns to the Test-Logic-Reset state.
16.3.1 TAP Communication Examples—IR-Scan and DR-Scan
Figure 16-3 and Figure 16-4 illustrate examples of communication between the host JTAG controller and the TAP of the
MAX31782. The host controls the TCK and TMS signals to move through the desired TAP states while accessing the
selected shift register through the TDI input and TDO output pair.
Figure 16-3. TAP Controller Debug Mode IR-Scan Example
NEW INSTRUCTION
INSTRUCTION REGISTER
TCK
TMS
TDI
TDO
CONTROL
STATE
IR SHIFT
REGISTER
IR PARALLEL
OUTPUT
REGISTER
SELECTED
TDO
ENABLE
BYPASS
DON'T CARE OR UNDEFINED
DON'T CARE OR UNDEFINED
DON'T CARE OR UNDEFINED
DON'T CARE OR UNDEFINED
TEST-LOGIC-RESET
RUN-TEST/IDLE
SELECT-DR-SCAN
SELECT-IR-SCAN
CAPTURE-IR
SHIFT-IR
SHIFT-IR
EXIT1-IR
EXIT1-IR
UPDATE-IR
RUN-TEST/IDLE
EXIT2-IR
PAUSE-IR
(26 paginas)
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