MPC8560 Integrated Processor Hardware Specifications, Rev. 5
Freescale Semiconductor
93
System Design Information
When data is held high, SW1 is closed (SW2 is open) and RP is trimmed until the voltage at the pad equals
OVDD/2. RP then becomes the resistance of the pull-up devices. RP and RN are designed to be close to each
other in value. Then, Z0 = (RP + RN)/2.
Figure 59. Driver Impedance Measurement
The output impedance of the RapidIO port drivers targets 200-
Ω differential resistance. 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 V1 = Rsource × Isource. Second, the output voltage is measured while driving logic
1 with an external precision differential termination resistor of value Rterm. The measured voltage is
V2 = 1/(1/R1 +1/R2)) × Isource. Solving for the output impedance gives Rsource = Rterm × (V1/V2 –1). The
drive current is then Isource =V1/Rsource.
Table 61 summarizes the signal impedance targets. The driver impedance are targeted at minimum VDD, nominal OVDD, 105°C.
Table 61. Impedance Characteristics
Impedance
Local Bus, Ethernet, DUART, Control,
Configuration, Power Management
PCI/PCI-X
DDR DRAM
RapidIO
Symbol
Unit
RN
43 Target
25 Target
20 Target
NA
Z0
W
RP
43 Target
25 Target
20 Target
NA
Z0
W
Differential
NA
200 Target
ZDIFF
W
Note: Nominal supply voltages. See Table 1, Tj = 105°C. OVDD
OGND
RP
RN
Pad
Data
SW1
SW2