System Design Information
The platform PLL ratio and e500 PLL ratio configuration pins are not equipped with these default pull-up
devices.
21.9
JTAG Configuration Signals
Correct operation of the JTAG interface requires configuration of a group of system control pins as
demonstrated in
Care must be taken to ensure that these pins are maintained at a valid deasserted
state under normal operating conditions as most have asynchronous behavior and spurious assertion will
give unpredictable results.
Boundary-scan testing is enabled through the JTAG interface signals. The TRST signal is optional in the
IEEE 1149.1 specification, but it is provided on all processors built on Power Architecture technology. The
device requires TRST to be asserted during power-on reset flow to ensure that the JTAG boundary logic
does not interfere with normal chip operation. While the TAP controller can be forced to the reset 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 in order
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
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
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
is common to
all known emulators.
21.9.1
Termination of Unused Signals
If the JTAG interface and COP header will not be 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
MPC8548E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 6
Freescale Semiconductor
133
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
