mpc7450 Freescale Semiconductor, Inc, mpc7450 Datasheet - Page 40

• Manufacturer Part Number: mpc7450
• Description: Mpc7450 Risc Microprocessor
• Manufacturer: Freescale Semiconductor, Inc

System Design Information
1.9.6
The MPC7450 processor bus and L3 I/O drivers are characterized over process, voltage, and temperature.
To measure Z
each resistor is varied until the pad voltage is OV
The output impedance is the average of two components, the resistances of the pull-up and pull-down
devices. When data is held low, SW2 is closed (SW1 is open), and R
pad equals OV
is closed (SW2 is open), and R
the resistance of the pull-up devices. R
(R
Table 18 summarizes the signal impedance results. The impedance increases with junction temperature and
is relatively unaffected by bus voltage.
1.9.7
The MPC7450 requires high-resistive (weak: 4.7 k ) pull-up resistors on several control pins of the bus
interface to maintain the control signals in the negated state after they have been actively negated and
released by the MPC7450 or other bus masters. These pins are: TS, ARTRY, SHDO, and SHD1.
Some pins designated as being for factory test must be pulled up to OV
device operation. For the MPC7450, 483 BGA, the pins that must be pulled up to OV
and TEST[0:5]; the pins that must be pulled down are: L1_TSTCLK and TEST[6].
40
P
+ R
N
)/2.
Output Buffer DC Impedance
Pull-Up/Pull-Down Resistor Requirements
0
DD
, an external resistor is connected from the chip pad to OV
/2. R
Z
0
Impedance
N
MPC7450 RISC Microprocessor Hardware Specifications
then becomes the resistance of the pull-down devices. When data is held high, SW1
Typical
Maximum
Freescale Semiconductor, Inc.
Figure 22. Driver Impedance Measurement
For More Information On This Product,
P
Data
is trimmed until the voltage at the pad equals OV
Table 18. Impedance Characteristics
V
DD
= 1.5 V, OV
P
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and R
Processor Bus
33–42
31–51
N
DD
are designed to be close to each other in value. Then, Z
DD
= 1.8 V ± 5%, T
/2 (see Figure 22).
Pad
R
R
j
OV
OGND
N
P
= 5°–85°C
DD
L3 Bus
34–42
32–44
SW2
SW1
N
DD
is trimmed until the voltage at the
or down to GND to ensure proper
DD
or GND. Then, the value of
DD
Unit
DD
/2. R
are: LSSD_MODE
P
then becomes
MOTOROLA
0
=