mpc8308 Freescale Semiconductor, Inc, mpc8308 Datasheet - Page 84

• Manufacturer Part Number: mpc8308
• Description: Mpc8308 Powerquicc Ii Pro Processor Hardware Specification
• Manufacturer: Freescale Semiconductor, Inc

System Design Information
The value of this resistance and the strength of the driver’s current source can be found by making two
measurements. First, the output voltage is measured while driving logic 1 without an external differential
termination resistor. The measured voltage is V
while driving logic 1 with an external precision differential termination resistor of value R
measured voltage is V
R
Table 60
nominal NV
23.6
The device provides the user with power-on configuration options that can be set through the use of
external pull-up or pull-down resistors of 4.7 KΩ on certain output pins (see customer-visible
configuration pins). These pins are generally used as output-only pins in normal operation.
While PORESET is asserted, these pins are treated as inputs. The value presented on these pins while
PORESET is asserted is latched when PORESET deasserts, at which time the input receiver is disabled
and the I/O circuit takes on its normal function. Careful board layout with stubless connections to these
pull-up/pull-down resistors coupled with the large value of the pull-up/pull-down resistor should minimize
the disruption of signal quality or speed for output pins thus configured.
84
term
× (V
summarizes the signal impedance targets. The driver impedance are targeted at minimum V
Note: Nominal supply voltages. See
Configuration Pin Muxing
Impedance
1
/V
DD
2
R
R
, 105°C.
N
P
– 1). The drive current is then I
MPC8308 PowerQUICC II Pro Processor Hardware Specification, Rev. 1
2
= (1/(1/R
Local Bus, Ethernet, DUART, Control,
Configuration, Power Management
Figure 55. Driver Impedance Measurement
1
Data
+ 1/R
Table 60. Impedance Characteristics
Table
2
42 Target
42 Target
)) × I
2, T
1
source
source
= R
j
= 105°C.
source
. Solving for the output impedance gives R
= V
1
× I
/R
Pad
R
source
R
source
NV
N
P
VSS
DD
. Second, the output voltage is measured
.
SW2
SW1
DDR DRAM
20 Target
20 Target
Symbol
Z
Z
0
0
Freescale Semiconductor
term
Unit
Ω
Ω
. The
source
=
DD
,