System Design Information
Correct operation of the JTAG interface requires configuration of a group of system control pins as
demonstrated in Figure 66. 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 gives
unpredictable results.
The following pins must NOT be pulled down during power-on reset: DMA_DACK[0:1], EC5_MDC,
HRESET_REQ, TRIG_OUT/READY_P0/QUIESCE, MSRCID[2:4], MDVAL, and ASLEEP. The
TEST_SEL pin must be set to a proper state during POR configuration. For more details, refer to the pinlist
table of the individual device.
21.7 Output Buffer DC Impedance
The MPC8572E drivers are characterized over process, voltage, and temperature. For all buses, the driver
2
is a push-pull single-ended driver type (open drain for I C).
To measure Z for the single-ended drivers, an external resistor is connected from the chip pad to OV
0
DD
or GND. Then, the value of each resistor is varied until the pad voltage is OV /2 (see Figure 64). The
DD
output impedance is the average of two components, the resistances of the pull-up and pull-down devices.
When data is held high, SW1 is closed (SW2 is open) and R is trimmed until the voltage at the pad equals
P
OV /2. R then becomes the resistance of the pull-up devices. R and R are designed to be close to each
DD
P
P
N
other in value. Then, Z = (R + R )/2.
0
P
N
OV
DD
R
N
SW2
SW1
Pad
Data
R
P
OGND
Figure 64. Driver Impedance Measurement
MPC8572E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 4
Freescale Semiconductor
128
FREESCALE [ Freescale ]
