Functional Description

31.5 Functional Description

31.5.1 JTAG Module

The JTAG module consists of a TAP controller state machine, which is responsible for generating all control signals that execute the JTAG instructions and read/write data registers.

31.5.2 TAP Controller

The TAP controller is a state machine that changes state based on the sequence of logical values on the TMS pin. Figure 31-3shows the machine’s states. The value shown next to each state is the value of the TMS signal sampled on the rising edge of the TCLK signal.

Asserting the TRST signal asynchronously resets the TAP controller to the test-logic-reset state. As Figure 31-3shows, holding TMS at logic 1 while clocking TCLK through at least five rising edges also causes the state machine to enter the test-logic-reset state, whatever the initial state.

MOTOROLA

Chapter 31. IEEE 1149.1 Test Access Port (JTAG)

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Motorola MCF5281, MCF5282 user manual Jtag Module, TAP Controller