PCI2060 datasheet(39/76 Pages) TI

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Principles of Operation

April 2005

SCPS096A

Table 3−14. JTAG Instructions and Op Codes

INSTRUCTION

OP CODE

DESCRIPTION

EXTEST

00000

Drives terminals from the boundary scan register

SAMPLE

00001

Samples I/O terminals

CLAMP

00100

Drives terminals from the boundary scan register and selects the bypass register for shifts.

HIGHZ

00101

Puts all outputs and I/O terminals except for the TDO terminal into a high-impedance state.

BYPASS

11111

Selects the bypass register for shifts

3.13.3

1-Bit Bypass Register

The 1-bit bypass register is a 1-bit shift register that provides a means for effectively bypassing the JTAG test

logic through a single-bit serial connection through the chip from TDI to TDO. At board-level testing, this helps

reduce overall length of the scan ring.

3.13.4

Boundary Scan Register

The boundary-scan register is a single-shift register-based path formed by boundary-scan cells placed at the

chip’s signal terminals. The register is accessed through the JTAG port’s TDI and TDO terminals.

3.13.4.1 Boundary-Scan Register Cells

Each boundary-scan cell operates in conjunction with the current instruction and the current state in the test

access port controller state machine. The function of the boundary-scan register cells is determined by the

associated terminals, as follows:

•

Input-only terminals—The boundary-scan cell is basically a 1-bit shift register. The cell supports sample

and shift functions.

•

Output-only terminals—The boundary-scan cell comprises a 1-bit shift register and an output multiplexer.

The cell supports the sample, shift, and drive output functions.

•

Bidirectional terminals—The boundary-scan cell is identical to the output-only terminal cell, but it captures

test data from the incoming data line. The cell supports sample, shift, drive output, and hold output

functions. It is used at all I/O terminals.

The information in Table 3−15 is for implementation of boundary scan interface signals to permit in-circuit

testing.

PCI2060 Datasheet(PDF) 39 Page - Texas Instruments

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