MPC755 datasheet(44/56 Pages) MOTOROLA

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MPC755 RISC Microprocessor Hardware Specifications, Rev. 6.1

Freescale Semiconductor

System Design Information

others use left-to-right then top-to-bottom, while still others number the pins counter clockwise from pin 1 (as with

an IC). Regardless of the numbering, the signal placement recommended in Figure 25 is common to all known

emulators.

The QACK signal shown in Figure 24 is usually connected to the PCI bridge chip in a system and is an input to the

MPC755 informing it that it can go into the quiescent state. Under normal operation this occurs during a low-power

mode selection. In order for COP to work, the MPC755 must see this signal asserted (pulled down). While shown

on the COP header, not all emulator products drive this signal. If the product does not, a pull-down resistor can be

populated to assert this signal. Additionally, some emulator products implement open-drain type outputs and can

only drive QACK asserted; for these tools, a pull-up resistor can be implemented to ensure this signal is deasserted

when it is not being driven by the tool. Note that the pull-up and pull-down resistors on the QACK signal are

mutually exclusive and it is never necessary to populate both in a system. To preserve correct power-down operation,

QACK should be merged via logic so that it also can be driven by the PCI bridge.

8.8 Thermal Management Information

This section provides thermal management information for the ceramic ball grid array (CBGA) package for

air-cooled applications. Proper thermal control design is primarily dependent on the system-level design—the heat

sink, airflow, and thermal interface material. To reduce the die-junction temperature, heat sinks may be attached to

the package by several methods—adhesive, spring clip to holes in the printed-circuit board or package, and

mounting clip and screw assembly; see Figure 25. This spring force should not exceed 5.5 pounds of force.

Figure 25 describes the package exploded cross-sectional view with several heat sink options.

Figure 25. Package Exploded Cross-Sectional View with Several Heat Sink Options

The board designer can choose between several types of heat sinks to place on the MPC755. There are several

commercially-available heat sinks for the MPC755 provided by the following vendors:

Aavid Thermalloy

603-224-9988

80 Commercial St.

Concord, NH 03301

Internet: www.aavidthermalloy.com

Adhesive or

Thermal Interface Material

Heat Sink

CBGA Package

Heat Sink

Clip

Printed-Circuit Board

Option

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