SN54LVTH18646A Datasheet, PDF (9/36 Pages) Texas Instruments – 3.3-V ABT SCAN TEST DEVICES WITH 18-BIT TRANSCEIVERS AND REGISTERS

SN54LVTH18646A, SN54LVTH182646A, SN74LVTH18646A, SN74LVTH182646A
3.3-V ABT SCAN TEST DEVICES
WITH 18-BIT TRANSCEIVERS AND REGISTERS
SCBS311D – MARCH 1994 – REVISED JUNE 1997
Shift-DR
Upon entry to the Shift-DR state, the data register is placed in the scan path between TDI and TDO, and on the
first falling edge of TCK, TDO goes from the high-impedance state to an active state. TDO enables to the logic
level present in the least-significant bit of the selected data register.
While in the stable Shift-DR state, data is serially shifted through the selected data register on each TCK cycle.
The first shift occurs on the first rising edge of TCK after entry to the Shift-DR state (i.e., no shifting occurs during
the TCK cycle in which the TAP controller changes from Capture-DR to Shift-DR or from Exit2-DR to Shift-DR).
The last shift occurs on the rising edge of TCK, upon which the TAP controller exits the Shift-DR state.
Exit1-DR, Exit2-DR
The Exit1-DR and Exit2-DR states are temporary states that end a data-register scan. It is possible to return
to the Shift-DR state from either Exit1-DR or Exit2-DR without recapturing the data register. On the first falling
edge of TCK after entry to Exit1-DR, TDO goes from the active state to the high-impedance state.
Pause-DR
No specific function is performed in the stable Pause-DR state, in which the TAP controller can remain
indefinitely. The Pause-DR state suspends and resumes data-register scan operations without loss of data.
Update-DR
If the current instruction calls for the selected data register to be updated with current data, such update occurs
on the falling edge of TCK, following entry to the Update-DR state.
Capture-IR
When an instruction-register scan is selected, the TAP controller must pass through the Capture-IR state. In
the Capture-IR state, the instruction register captures its current status value. This capture operation occurs
on the rising edge of TCK, upon which the TAP controller exits the Capture-IR state. For the ’LVTH18646A and
’LVTH182646A, the status value loaded in the Capture-IR state is the fixed binary value 10000001.
Shift-IR
Upon entry to the Shift-IR state, the instruction register is placed in the scan path between TDI and TDO, and
on the first falling edge of TCK, TDO goes from the high-impedance state to the active state. TDO enables to
the logic level present in the least-significant bit of the instruction register.
While in the stable Shift-IR state, instruction data is serially shifted through the instruction-register on each TCK
cycle. The first shift occurs on the first rising edge of TCK after entry to the Shift-IR state (i.e., no shifting occurs
during the TCK cycle in which the TAP controller changes from Capture-IR to Shift-IR or from Exit2-IR to
Shift-IR). The last shift occurs on the rising edge of TCK, upon which the TAP controller exits the Shift-IR state.
Exit1-IR, Exit2-IR
The Exit1-IR and Exit2-IR states are temporary states that end an instruction-register scan. It is possible to
return to the Shift-IR state from either Exit1-IR or Exit2-IR without recapturing the instruction register. On the
first falling edge of TCK after entry to Exit1-IR, TDO goes from the active state to the high-impedance state.
Pause-IR
No specific function is performed in the stable Pause-IR state, in which the TAP controller can remain
indefinitely. The Pause-IR state suspends and resumes instruction-register scan operations without loss
of data.
Update-IR
The current instruction is updated and takes effect on the falling edge of TCK, following entry to the
Update-IR state.
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