mpc8536e Freescale Semiconductor, Inc, mpc8536e Datasheet - Page 118

• Manufacturer Part Number: mpc8536e
• Description: Mpc8536e Powerquicctm Iii Integrated Processor Hardware Specifications
• Manufacturer: Freescale Semiconductor, Inc

Configuration Pin Muxing
Impedance
Note: Nominal supply voltages. See
3.9
The MPC8536E provides the user with power-on configuration options which can be set through the use of external pull-up or
pull-down resistors of 4.7 k Ω on certain output pins (see customer visible configuration pins). These pins are generally used as
output only pins in normal operation.
While HRESET is asserted however, these pins are treated as inputs. The value presented on these pins while HRESET is
asserted, is latched when HRESET deasserts, at which time the input receiver is disabled and the I/O circuit takes on its normal
function. Most of these sampled configuration pins are equipped with an on-chip gated resistor of approximately 20 k Ω . This
value should permit the 4.7-k Ω resistor to pull 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.
3.10
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 unpredicatable 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
target can drive HRESET as well.
118
R
R
N
P
Configuration Pin Muxing
JTAG Configuration Signals
Control, Configuration, Power
Local Bus, Ethernet, DUART,
MPC8536E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 2
Management
45 Target
45 Target
Figure 78
Table
allows the COP port to independently assert HRESET or TRST, while ensuring that the
Table 81. Impedance Characteristics
1.
45 Target (cfg_pci_impd=1)
25 Target (cfg_pci_impd=0)
45 Target (cfg_pci_impd=1)
25 Target (cfg_pci_impd=0)
PCI
18 Target (full strength mode)
36 Target (full strength mode)
18 Target (full strength mode)
36 Target (full strength mode)
DDR DRAM
Freescale Semiconductor
Symbol Unit
Z
Z
Figure
0
0
Ω
Ω
78.