Motorola MSC8101 ADS User's Guide Page 233

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MSC8101 User’s Guide 12-1
Chapter 12
EOnCE/JTAG
This chapter presents examples of how the EOnCE port can be used for system-level
debugging of real-time systems. The following examples are presented:
Reading/writing EOnCE registers through JTAG
Executing a single instruction through JTAG
Writing to the EOnCE Receive Register (ERCV)
Reading from the EOnCE Transmit Register (ETRSMT)
Downloading software
Reading/writing the trace buffer
Using the EOnCE to perform profiling functions
12.1 EOnCE/JTAG Basics
In order to access the EOnCE through JTAG, you need to know about the JTAG scan
paths, the JTAG instructions, the EOnCE control register value, and the CORE_CMD
value. This section gives you these basics, starting with the scan paths.
The host controller transitions from one Test Access Port (TAP) controller state to another
by taking one of the following scan paths:
Select-IR JTAG scan path. Used when the host sends the JTAG instructions shown
in Table 12-2 to the MSC8101.
Select-DR JTAG scan path. Used when the host sends data to the MSC8101 or
receives status information from the MSC8101.
Figure 12-1 shows the TAP controller state machine, and Table 12-1 shows the states
associated with each scan path. The Test Mode Select (
TMS) pin determines whether an
instruction register scan or a data register scan is performed. At power-up or during
normal operation of the host, the TAP is forced into the Test-Logic-Reset state by driving
TMS high for five or more Test Clock (TCK) cycles. When test access is required, TMS is set
low to cause the TAP to exit the Test-Logic-Reset and move through the appropriate
states. From the Run-Test/Idle state, an instruction register scan or a data register scan can
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