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Section 15 User Debugging Interface (H-UDI)
Rev. 4.00 Sep. 14, 2005 Page 471 of 982
REJ09B0023-0400
15.5 Boundary Scan
A command can be set in SDIR by the H-UDI to place the H-UDI pins in the boundary scan mode
stipulated by JTAG.
15.5.1 Supported Instructions
This LSI supports the three essential instructions defined in the JTAG standard (BYPASS,
SAMPLE/PRELOAD, and EXTEST) and three option instructions (IDCODE, CLAMP, and
HIGHZ).
BYPASS: The BYPASS instruction is an essential standard instruction that operates the bypass
register. This instruction shortens the shift path to speed up serial data transfer involving other
chips on the printed circuit board. While this instruction is executing, the test circuit has no effect
on the system circuits. The upper four bits of the instruction code are B'1111.
SAMPLE/PRELOAD: The SAMPLE/PRELOAD instruction inputs values from this LSI's
internal circuitry to the boundary scan register, outputs values from the scan path, and loads data
onto the scan path. When this instruction is executing, this LSI's input pin signals are transmitted
directly to the internal circuitry, and internal circuit values are directly output externally from the
output pins. This LSI's system circuits are not affected by execution of this instruction. The upper
four bits of the instruction code are B'0100.
In a SAMPLE operation, a snapshot of a value to be transferred from an input pin to the internal
circuitry, or a value to be transferred from the internal circuitry to an output pin, is latched into the
boundary scan register and read from the scan path. Snapshot latching is performed in
synchronization with the rise of TCK in the Capture-DR state. Snapshot latching does not affect
normal operation of this LSI.
In a PRELOAD operation, an initial value is set in the parallel output latch of the boundary scan
register from the scan path prior to the EXTEST instruction. Without a PRELOAD operation,
when the EXTEST instruction was executed an undefined value would be output from the output
pin until completion of the initial scan sequence (transfer to the output latch) (with the EXTEST
instruction, the parallel output latch value is constantly output to the output pin).