MPC8347E datasheet(101/108 Pages) FREESCALE

101 / 108 page

MPC8347EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 3

Freescale Semiconductor

101

System Design Information

Figure 42. Driver Impedance Measurement

Two measurements give the value of this resistance and the strength of the driver current source. 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 68 summarizes the signal impedance targets. The driver impedance are targeted at minimum VDD,

nominal OVDD, 105°C.

21.6

Configuration Pin Multiplexing

The MPC8347EA power-on configuration options can be set through external pull-up or pull-down

resistors of 4.7 k

Ω on certain output pins (see the customer-visible configuration pins). These pins are used

as output only pins in normal operation.

However, while HRESET is asserted, these pins are treated as inputs, and the value on these pins is latched

when PORESET deasserts. Then 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

Table 68. Impedance Characteristics

Impedance

Local Bus, Ethernet,

DUART, Control,

Configuration, Power

Management

PCI Signals

(not including PCI

output clocks)

PCI Output Clocks

(including

PCI_SYNC_OUT)

DDR DRAM

Symbol

Unit

42 Target

25 Target

42 Target

20 Target

42 Target

25 Target

42 Target

20 Target

Differential

ZDIFF

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

OVDD

OGND

Pad

Data

SW1

SW2

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