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CHAPTER 8 JTAG BOUNDARY SCAN
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8.7.1 BYPASS Instruction
This instruction is specified by setting "11" or "10" as the instruction data. While the TAP controller is in the
Shift-DR state, this instruction is used to enable selection of the bypass register (positioned between the JDI
and JDO pins and used for serial access) only.
When this instruction is selected, the JTAG boundary scan circuit does not affect the operation of the
μ
PD98405.
This instruction is selected while the TAP controller is in the Test-Logic-Reset state.
8.7.2 EXTEST Instruction
This instruction is specified by setting "00" as the instruction data. While the TAP controller is in the Shift-
DR state, this instruction is used to enable selection of the boundary scan register for serial access between
the JDI and JDO pins.
When this instruction is selected:
Based on the data shifted into the boundary scan register, the states of all the signals driven from the
system output pins are all clearly defined. While the TAP controller is in the Update-DR state, conversion
is performed only at the falling edge of the signal being input to the JCK pin.
While the TAP controller is in the Capture-DR state, the states of all the signals input from the system
input pins are loaded into the boundary scan register at a rising edge of the signal being input to the JCK
pin.
8.7.3 Boundary Scan Data Bit Setting
In response to customer requests, NEC has made available the BSDL (Boundary Scan Description
Language) reference file for the
μ
PD98405. To obtain this file, contact the NEC Semiconductor Technical
Hotline.