System Design Information
state using only the TCK and TMS signals, generally systems assert TRST during the power-on reset flow.
Simply tying TRST to HRESET is not practical because the JTAG interface is also used for accessing the
common on-chip processor (COP), which implements the debug interface to the chip.
The COP function of these processors allow a remote computer system (typically, a PC with dedicated
hardware and debugging software) to access and control the internal operations of the processor. The COP
interface connects primarily through the JTAG port of the processor, with some additional status
monitoring signals. The COP port requires the ability to independently assert HRESET or TRST to fully
control the processor. If the target system has independent reset sources, such as voltage monitors,
watchdog timers, power supply failures, or push-button switches, then the COP reset signals must be
merged into these signals with logic.
The arrangement shown in Figure 66 allows the COP port to independently assert HRESET or TRST,
while ensuring that the target can drive HRESET as well.
The COP interface has a standard header, shown in Figure 65, for connection to the target system, and is
based on the 0.025" square-post, 0.100" centered header assembly (often called a Berg header). The
connector typically has pin 14 removed as a connector key.
The COP header adds many benefits such as breakpoints, watchpoints, register and memory
examination/modification, and other standard debugger features. An inexpensive option can be to leave
the COP header unpopulated until needed.
There is no standardized way to number the COP header; so emulator vendors have issued many different
pin numbering schemes. Some COP headers are numbered top-to-bottom then left-to-right, while others
use left-to-right then top-to-bottom. Still others number the pins counter-clockwise from pin 1 (as with an
IC). Regardless of the numbering scheme, the signal placement recommended in Figure 65 is common to
all known emulators.
21.9.1 Termination of Unused Signals
If the JTAG interface and COP header is not used, Freescale recommends the following connections:
•
TRST should be tied to HRESET through a 0 kΩ isolation resistor so that it is asserted when the
system reset signal (HRESET) is asserted, ensuring that the JTAG scan chain is initialized during
the power-on reset flow. Freescale recommends that the COP header be designed into the system
as shown in Figure 66. If this is not possible, the isolation resistor allows future access to TRST in
case a JTAG interface may need to be wired onto the system in future debug situations.
•
No pull-up/pull-down is required for TDI, TMS, TDO or TCK.
MPC8572E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 4
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Freescale Semiconductor
FREESCALE [ Freescale ]
