MPC8548E Freescale, MPC8548E Datasheet - Page 132

• Manufacturer Part Number: MPC8548E
• Description: Integrated Processor
• Manufacturer: Freescale

System Design Information
www.DataSheet4U.com
the configuration pin to a valid logic low level. The pull-up resistor is enabled only during HRESET (and
for platform/system clocks after HRESET deassertion to ensure capture of the reset value). When the input
receiver is disabled the pull-up is also, thus allowing functional operation of the pin as an output with
minimal signal quality or delay disruption. The default value for all configuration bits treated this way has
been encoded such that a high voltage level puts the device into the default state and external resistors are
needed only when non-default settings are required by the user.
Careful board layout with stubless connections to these pull-down resistors coupled with the large value
of the pull-down resistor should minimize the disruption of signal quality or speed for output pins thus
configured.
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
Figure
62. 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
Figure 62
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
61, 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
MPC8548E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 4
132
Freescale Semiconductor