Datasheet

SN74ABT18502
SCAN TEST DEVICE
WITH 18-BIT REGISTERED BUS TRANSCEIVER
SCBS753 – FEBRUARY 2002
7
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
Exit1-DR, Exit2-DR
The Exit1-DR and Exit2-DR states are temporary states used to end a DR scan. It is possible to return to the
Shift-DR state from either Exit1-DR or Exit2-DR without recapturing the DR.
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 provides the capability of suspending and resuming DR scan operations
without loss of data.
Update-DR
If the current instruction calls for the selected DR 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 IR scan is selected, the TAP controller must pass through the Capture-IR state. In the Capture-IR state,
the IR 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 SN74ABT18502, 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 IR 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 LSB of the IR.
While in the stable Shift-IR state, instruction data is serially shifted through the IR 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 used to end an IR scan. It is possible to return to the
Shift-IR state from either Exit1-IR or Exit2-IR without recapturing the IR.
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 provides the capability of suspending and resuming IR 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.