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MPC8343VRAGDB 数据表(PDF) 74 Page - Freescale Semiconductor, Inc |
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MPC8343VRAGDB 数据表(HTML) 74 Page - Freescale Semiconductor, Inc |
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74 / 79 page ![]() MPC8343EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 10 74 Freescale Semiconductor System Design Information 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 38. 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 61 summarizes the signal impedance targets. The driver impedance are targeted at minimum VDD, nominal OVDD, 105°C. 21.6 Configuration Pin Multiplexing The MPC8343EA 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. Table 61. 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 RN 42 Target 25 Target 42 Target 20 Target Z0 W RP 42 Target 25 Target 42 Target 20 Target Z0 W Differential NA NA NA NA ZDIFF W Note: Nominal supply voltages. See Table 1, Tj = 105°C. OVDD OGND RP RN Pad Data SW1 SW2 |
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