SN54ABT8652, SN74ABT8652

SCAN TEST DEVICES

WITH OCTAL BUS TRANSCEIVERS AND REGISTERS

SCBS122F – AUGUST 1992 – REVISED DECEMBER 1996

8

POST OFFICE BOX 655303

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, then 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 ’ABT8652, 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 an 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.