31 of 47

March 31, 2008

IDT80KSW0004

Datasheet

The output enable cells are also output cells. The simplified logic appears in the figure below.

Figure 23 Diagram of Output Enable Cell

The bidirectional cells are composed of only two boundary scan cells. They contain one output enable cell and one capture cell, which contains only

one register. The input to this single register is selected via a mux that is selected by the output enable cell when EXTEST is disabled. When the

Output Enable Cell is driving a high out to the pad (which enables the pad for output) and EXTEST is disabled, the Capture Cell will be configured to

capture output data from the core to the pad.

However, in the case where the Output Enable Cell is low (signifying a tri-state condition at the pad) or EXTEST is enabled, the Capture Cell will

capture input data from the pad to the core. The configuration is shown graphically in the figure below.

Figure 24 Diagram of Bidirectional Cell

Instruction Register (IR)

The Instruction register allows an instruction to be shifted serially into the CPS-12 at the rising edge of TCK. The instruction is then used to select the

test to be performed or the test register to be accessed, or both. The instruction shifted into the register is latched at the completion of the shifting

process, when the TAP controller is at the Update-IR state.

DQ

D

Q

From Core

Data from previous cell

EXTEST

To output enable

clock_dr

shift_dr

update_dr

Output Enable

To next cell

From previous cell

Output Enable Cell

Output enable from core

EXTEST

Output from core

Input to core

Capture Cell

To next cell

I/O

Pin