MPC970

MOTOROLA

TIMING SOLUTIONS

BR1333 — Rev 6

14

Driving the PowerPC 603, PowerPC 604 and Pentium

Microprocessors

The PowerPC 603, PowerPC 604 and Pentium

processors differ from the MPC 601 processor in that the

processor input clocks are at the same frequency as the

processor bus. A typical system for these processors will

include 8 – 16 clock loads on the processor bus. When the

MPC970 is taken out of the MPC601_Clk mode there are a

total of 8 “non PCI_CLK” outputs which can be run at the

processor bus speeds for these microprocessors. Since

each output can drive two series terminated transmission

lines the MPC970 can support point to point clock distribution

for up to 16 loads on the processor bus. In addition there will

be 7 PCI_CLK outputs which can drive up to 14 loads on the

PCI bus.

If more clock loads are present on the processor bus the

PCI_CLKs can be configured to drive processor bus clock

loads in addition to the BCLKs or alternatively the clocking

roles of the BCLKs and PCI_CLKs can be reversed. Table 3

illustrates some useful frequency combinations for driving

PowerPC 603, PowerPC 604 or Pentium microprocessor

based systems.

Table Table 5. Common PowerPC 603, PowerPC 604

and Pentium System Frequencies

2x_PCLK

PCLK

BCLK

PCI_CLK

80

80

80(1x)

26(1/3x)

75

75

75(1x)

25(1/3x)

66

66

66(1x)

33(1/2x)

66

66

66(1x)

66(1x)

66

66

33(1/2x)

66(PCLKEN)

60

60

60(1x)

30(1/2x)