
SN54ABT8996, SN74ABT8996
10-BIT ADDRESSABLE SCAN PORTS
MULTIDROP-ADDRESSABLE IEEE STD 1149.1 (JTAG) TAP TRANSCEIVERS
SCBS489C – AUGUST 1994 – REVISED APRIL 1999
10
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
Test-Logic-Reset
The ASP TAP-state monitor powers up in the Test-Logic-Reset state. Alternatively, the ASP can be forced
asynchronously to this state by assertion of its PTRST input. In the stable Test-Logic-Reset state, the ASP is
enabled to receive and respond to shadow protocols. The ASP does not recognize the TSA in this state.
For a target device in the stable Test-Logic-Reset state, the test logic is reset and is disabled so that the normal
logic function of the device is performed. The instruction register is reset to an opcode that selects the optional
IDCODE instruction, if supported, or the BYPASS instruction. Certain data registers also can be reset to their
power-up values.
Run-Test/Idle
In the stable Run-Test/Idle state, the ASP is enabled to receive and respond to shadow protocols. The ASP does
not recognize the TSA in this state.
For a target device, Run-Test/Idle is a stable state in which the test logic can be actively running a test or can
be idle.
Select-DR-Scan, Select-lR-Scan
The ASP is not enabled to receive and respond to shadow protocols in the Select-DR-Scan and
Select-lR-Scan states.
For a target device, no specific function is performed in the Select-DR-Scan and Select-lR-Scan states, and the
TAP controller exits either of these states on the next TCK cycle. These states allow the selection of either
data-register scan or instruction-register scan.
Capture-DR
The ASP is not enabled to receive and respond to shadow protocols in the Capture-DR state.
For a target device in the Capture-DR state, the selected data register can capture a data value as specified
by the current instruction. Such capture operations occur on the rising edge of TCK, upon which the Capture-DR
state is exited.
Shift-DR
The ASP is not enabled to receive and respond to shadow protocols in the Shift-DR state.
For a target device, upon entry to the Shift-DR state, the selected 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 outputs 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.
Exit1-DR, Exit2-DR
The ASP is not enabled to receive and respond to shadow protocols in the Exit1-DR and Exit2-DR states.
For a target device, 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
In the stable Pause-DR 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-DR state. The Pause-DR state
suspends and resumes data-register scan operations without loss of data.