IDT 89HPES12N3, Руководство пользователя

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IDT JTAG Boundary Scan Instruction Register (IR)
PES12N3 User Manual 11 - 7 June 7, 2006
Notes
EXTEST
The external test (EXTEST) instruction is used to control the boundary scan register, once it has been
initialized using the SAMPLE/PRELOAD instruction. Using EXTEST, the user can then sample inputs from
or load values onto the external pins of the PES12N3. Once this instruction is selected, the user then uses
the SHIFT-DR TAP controller state to shift values into the boundary scan chain. When the TAP controller
passes through the UPDATE-DR state, these values will be latched onto the output pins or into the output
enables.
SAMPLE/PRELOAD
The sample/preload instruction has a dual use. The primary use of this instruction is for preloading the
boundary scan register prior to enabling the EXTEST instruction. Failure to preload will result in unknown
random data being driven onto the output pins when EXTEST is selected. The secondary function of
SAMPLE/PRELOAD is for sampling the system state at a particular moment. Using the SAMPLE function,
the user can halt the device at a certain state and shift out the status of all of the pins and output enables at
that time.
BYPASS
The BYPASS instruction is used to truncate the boundary scan register to a single bit in length. During
system level use of the JTAG, the boundary scan chains of all the devices on the board are connected in
series. In order to facilitate rapid testing of a given device, all other devices are put into BYPASS mode.
Therefore, instead of having to shift 499 times to get a value through the PES12N3, the user only needs to
shift one time to get the value from JTAG_TDI to JTAG_TDO. When the TAP controller passes through the
CAPTURE-DR state, the value in the BYPASS register is updated to be 0.
If the device being used does not have a DEVICE_ID register, then the BYPASS instruction will automat-
ically be selected into the instruction register whenever the TAP controller is reset. Therefore, the first value
that will be shifted out of a device without a DEVICE_ID register is always 0. Devices such as the PES12N3
that include a DEVICE_ID register will automatically load the DEVICE_ID instruction when the TAP
controller is reset, and they will shift out an initial value of 1. This is done to allow the user to easily distin-
guish between devices having DEVICE_ID registers and those that do not.
HIGHZ Tri-states all output and bidirectional boundary scan cells. 000011
RESERVED Behaviorally equivalent to the BYPASS instruction as per the IEEE
Std. 1149.1 specification. However, the user is advised to use the
explicit BTPASS instruction. 000100 —
100011
UNUSED The unused instructions are behaviorally equivalent to the BYPASS
instruction as per the IEEE Std. 1149.1 specification. However, the
user is advised to use the explicit BYPASS instruction, as the internal
usage of these currently unused instructions could possibly vary in
future implementations of the device. 100100 —
101100
VALIDATE Automatically loaded into the instruction register whenever the TAP
controller passes through the CAPTURE-IR state. The lower two bits
‘01’ are mandated by the IEEE Std. 1149.1 specification. 101101
UNUSED Same as the other UNUSED instruction above. 101110 —
111100
RESERVED Same as the other RESERVED instruction above. 111101
CLAMP Provides JTAG users with the option to bypass the part’s JTAG con-
troller while keeping the part outputs controlled similar to EXTEST. 111110
BYPASS The BYPASS instruction is used to truncate the boundary scan regis-
ter as a single bit in length. 111111
Instruction Definition Opcode
Table 11.3 Instructions Supported by PES12N3’s JTAG Boundary Scan (Part 2 of 2)