MPC8280 datasheet(541/1386 Pages) FREESCALE

541 / 1386 page

IEEE 1149.1 Test Access Port

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

13-7

The parallel output of the instruction register is set to all ones in the test-logic-reset controller state. Notice

that this preset state is equivalent to the BYPASS instruction. During the capture-IR controller state, the

parallel inputs to the instruction shift register are loaded with the CLAMP command code.

13.5

MPC8280 Restrictions

The control afforded by the output enable signals using the boundary-scan register and the EXTEST

instruction requires a compatible circuit-board test environment to avoid device-destructive

configurations. The user must avoid situations in which the MPC8280’s output drivers are enabled into

actively driven networks.

13.6

Nonscan Chain Operation

In nonscan chain operation, the TCK input does not include an internal pull-up resistor and should be tied

high or low to preclude mid-level inputs.

To ensure that the scan chain test logic is kept transparent to the system logic, the TAP controller is forced

into the test-logic-reset state. This is done inside the chip by connecting TRST to PORESET

TMS should remain logic high, so that the TAP controller does not leave the test-logic-reset state.

HI–Z

Provided as a manufacturer’s optional public instruction to

avoid back driving the output pins during circuit-board testing.

When HI-Z is invoked all output drivers, including the two-state

drivers, are turned off (high impedance). The instruction

selects the bypass register.

100

CLAMP and

BYPASS

CLAMP selects the single-bit bypass register as shown in the

BYPASS instruction figure above, and the state of all signals

driven from the system output pins is completely defined by the

data previously shifted into the boundary scan register. For

example, using the SAMPLE/PRELOAD instruction.

1 B0 (lsb) is shifted first.

Table 13-2. Instruction Decoding (continued)

Code1

Instruction

Description

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