SN54ABT8996, SN74ABT8996

10-BIT ADDRESSABLE SCAN PORTS

MULTIDROP-ADDRESSABLE IEEE STD 1149.1 (JTAG) TAP TRANSCEIVERS

SCBS489C – AUGUST 1994 – REVISED APRIL 1999

11

POST OFFICE BOX 655303

Update-DR

The ASP is not enabled to receive and respond to shadow protocols in the Update-DR state.

For a target device, 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

The ASP is not enabled to receive and respond to shadow protocols in the Capture-IR state.

For a target device 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 Capture-IR state is exited.

Shift-IR

The ASP is not enabled to receive and respond to shadow protocols in the Shift-IR state.

For a target device, 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 an active state.

TDO outputs 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.

Exit1-IR, Exit2-IR

The ASP is not enabled to receive and respond to shadow protocols in the Exit1-IR and Exit2-IR states.

For target devices, 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

In the stable Pause-IR state, the ASP is enabled to receive and respond to shadow protocols. Additionally, the

TSA can be recognized in this state.

For target devices, 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 ASP is not enabled to receive and respond to shadow protocols in the Update-IR state.

For target devices, the current instruction is updated and takes effect on the falling edge of TCK, following entry

to the Update-IR state.