Chapter 35 IEEE 1149.1 Test Access Port Controller (JTAGC)
MPC5602P Microcontroller Reference Manual, Rev. 4
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Freescale Semiconductor
35.4
Features
The JTAGC is compliant with the IEEE 1149.1-2001 standard, and supports the following features:
•
IEEE 1149.1-2001 Test Access Port (TAP) interface
•
Four pins (TDI, TMS, TCK, and TDO)—see
Section 35.6, “External signal description.
•
A 5-bit instruction register that supports several IEEE 1149.1-2001 defined instructions, as well as
several public and private MCU specific instructions.
•
Test data registers: a bypass register, a boundary scan register, and a device identification register.
•
A TAP controller state machine that controls the operation of the data registers, instruction register,
and associated circuitry.
35.5
Modes of operation
The JTAGC uses a power-on reset indication as its primary reset signals. Several IEEE 1149.1-2001
defined test modes are supported, as well as a bypass mode.
35.5.1
Reset
The JTAGC is placed in reset when the TAP controller state machine is in the TEST-LOGIC-RESET state.
The TEST-LOGIC-RESET state is entered upon the assertion of the power-on reset signal, or through TAP
controller state machine transitions controlled by TMS. Asserting power-on reset results in asynchronous
entry into the reset state. While in reset, the following actions occur:
•
The TAP controller is forced into the test-logic-reset state, thereby disabling the test logic and
allowing normal operation of the on-chip system logic to continue unhindered.
•
The instruction register is loaded with the IDCODE instruction.
In addition, execution of certain instructions can result in assertion of the internal system reset. These
instructions include EXTEST, CLAMP, and HIGHZ.
35.5.2
IEEE 1149.1-2001 defined test modes
The JTAGC supports several IEEE 1149.1-2001 defined test modes. The test mode is selected by loading
the appropriate instruction into the instruction register while the JTAGC is enabled. Supported test
instructions include EXTEST, HIGHZ, CLAMP, SAMPLE and SAMPLE/PRELOAD. Each instruction
defines the set of data registers that can operate and interact with the on-chip system logic while the
instruction is current. Only one test data register path is enabled to shift data between TDI and TDO for
each instruction.
The boundary scan register is enabled for serial access between TDI and TDO when the EXTEST,
SAMPLE or SAMPLE/PRELOAD instructions are active. The single-bit bypass register shift stage is
enabled for serial access between TDI and TDO when the HIGHZ, CLAMP or reserved instructions are
active. The functionality of each test mode is explained in more detail in