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19
19.3 JTAG Registers
19.3.1 Instruction Register (JTAGIR)
The Instruction Register (JTAGIR) is a 6-bit register to hold instruction code. This register is set in
IR path sequence. The instructions set in this register determine the data register to be selected in
the subsequent DR path sequence.
When test is reset (to initialize the test circuit), the initial value of this register is b'000010 (IDCODE
instruction). After a test reset, the IDCODE Register is selected as the data register until an
instruction code is set by an external device. In "Capture-IR" state, this register always has
b'110001 (fixed value) loaded into it. Therefore, when in "Shift-IR" state, no matter what value was
set in this register, b'110001 is always output from the JTDO pin (sequentially beginning with LSB).
However, this value normally is not handled as instruction code.
Shown below is outside the scope of guaranteed operations. Note that if this operation is
performed, the device may inadvertently handle b'110001 as instruction code, which makes it
unable to operate normally.
[Capture-IR] → [Exit1-IR] → [Update-IR]
The 32170's JTAG interface supports the following instructions:
• Three instructions stipulated as essential in IEEE 1149.1 (EXTEST, SAMPLE/PRELOAD,
BYPASS)
• Device ID register access instruction (IDCODE)
Table 19.3.1 JTAG Instruction List
Instruction Code Abbreviation
b'000000
b'000001
b'000010
b'111111
Note 1 : Do not set any other instruction code.
Note 2 : For details about "IR path sequence," "DR path sequence," "Test reset," "Capture-IR" state, "Shift-IR"
state, "Exit1-IR" state, and "Update-IR" state, refer to Section 19.4.
Operation
EXTEST
Tests circuit/board-level connections outside the chip.
SAMPLE/PRELOAD
Samples operating circuit status and outputs the sampled status
from JTDO pin, while at the same time entering the data used for
boundary-scan test from the JTDI pin and presets it in Boundary
Scan Register.
IDCODE
Selects ID Code Register and outputs device and manufacturer
identification data from JTDO pin.
BYPASS
Selects Bypass Register and inspects or sets data.
19-4
JTAG
19.3 JTAG Registers
Ver.0.10
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