MPC8540CPX667JC datasheet(91/104 Pages) FREESCALE

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MPC8540 Integrated Processor Hardware Specifications, Rev. 4

Freescale Semiconductor

System Design Information

Figure 52. 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 60 summarizes the signal impedance targets. The driver impedance are targeted at minimum VDD,

nominal OVDD, 105°C.

17.6 Configuration Pin Muxing

The MPC8540 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.

Table 60. Impedance Characteristics

Impedance

Local Bus, Ethernet,

DUART, Control,

Configuration, Power

Management

PCI/PCI-X

DDR DRAM

RapidIO

Symbol

Unit

43 Target

25 Target

20 Target

43 Target

25 Target

20 Target

Differential

200 Target

ZDIFF

Note: Nominal supply voltages. See Table 1, Tj = 105°C.

OVDD

OGND

Pad

Data

SW1

SW2

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