MPC870 datasheet(15/84 Pages) FREESCALE

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MPC875/MPC870 Hardware Specifications, Rev. 3.0

PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE

Freescale Semiconductor

Layout Practices

10 Layout Practices

Each VDD pin on the MPC875/870 should be provided with a low-impedance path to the board’s supply. Each GND

pin should likewise be provided with a low-impedance path to ground. The power supply pins drive distinct groups

of logic on chip. The VDD power supply should be bypassed to ground using at least four 0.1-µF bypass capacitors

located as close as possible to the four sides of the package. Each board designed should be characterized and

additional appropriate decoupling capacitors should be used if required. The capacitor leads and associated printed

circuit traces connecting to chip VDD and GND should be kept to less than half an inch per capacitor lead. At a

minimum, a four-layer board employing two inner layers as VDD and GND planes should be used.

All output pins on the MPC875/870 have fast rise and fall times. Printed circuit (PC) trace interconnection length

should be minimized in order to minimize undershoot and reflections caused by these fast output switching times.

This recommendation particularly applies to the address and data buses. Maximum PC trace lengths of six inches

are recommended. Capacitance calculations should consider all device loads as well as parasitic capacitances due to

the PC traces. Attention to proper PCB layout and bypassing becomes especially critical in systems with higher

capacitive loads because these loads create higher transient currents in the VDD and GND circuits. Pull up all unused

inputs or signals that will be inputs during reset. Special care should be taken to minimize the noise levels on the

PLL supply pins. For more information, please refer to Section 14.4.3, “Clock Synthesizer Power (VDDSYN,

VSSSYN, VSSSYN1),” of the MPC885 PowerQUICC Family User’s Manual.

11 Bus Signal Timing

The maximum bus speed supported by the MPC875/870 is 80 MHz. Higher-speed parts must be operated in

half-speed bus mode (for example, an MPC875/870 used at 133 MHz must be configured for a 66 MHz bus). Table 8

shows the frequency ranges for standard part frequencies in 1:1 bus mode, and Table 9 shows the frequency ranges

for standard part frequencies in 2:1 bus mode.

PCDIR

(Port C data direction register)

PCDIR[4:5]

PCDIR[8:9]

PCDIR[14]

PDPAR

(Port D pin assignment register)

PDPAR[3:7]

PDPAR[9:5]

PDDIR

(Port D data direction register)

PDDIR[3:7]

PDDIR[9:15]

Table 8. Frequency Ranges for Standard Part Frequencies (1:1 Bus Mode)

Part Frequency

66 MHz

80 MHz

Min

Max

Min

Max

Core frequency

66.67

Bus frequency

66.67

Table 7. Mandatory Reset Configuration of MPC875/870 (continued)

Field

Value

(binary)

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