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MPC750A RISC Microprocessor Hardware Specications
System Design Information
1.8.6 Pull-up Resistor Requirements
The MPC750 requires high-resistive (weak: 10 K
) pull-up resistors on several control signals of the bus
interface to maintain the control signals in the negated state after they have been actively negated and
released by the MPC750 or other bus masters. These signals are TS, ABB, DBB, and ARTRY.
In addition, the MPC750 has one open-drain style output that requires a pull-up resistors (weak or
stronger: 4.7 K
–10 K) if it is used by the system. This signal is CKSTP_OUT.
During inactive periods on the bus, the address and transfer attributes on the bus are not driven by any
master and may oat in the high-impedance state for relatively long periods of time. Since the MPC750
must continually monitor these signals for snooping, this oat condition may cause excessive power draw
by the input receivers on the MPC750 or by other receivers in the system. It is recommended that these
signals be pulled up through weak (10 K
) pull-up resistors or restored in some manner by the system.
The snooped address and transfer attribute inputs are A[0–31], AP[0–3], TT[0–4], TBST, and GBL.
The data bus input receivers are normally turned off when no read operation is in progress and do not
require pull-up resistors on the data bus. Other data bus receivers in the system, however, may require
pullups, or that those signals be otherwise driven by the system during inactive periods. The data bus
signals are
DH[0–31], DL[0–31], DP[0–7].
If address or data parity is not used by the system, and the respective parity checking is disabled through
HID0, the input receivers for those pins are disabled, and those pins do not require pull-up resistors and
should be left unconnected by the system. If all parity generation is disabled through HID0, then all parity
checking should also be disabled through HID0, and all parity pins may be left unconnected by the system.
No pull-up resistors are normally required for the L2 interface.
1.8.7 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 upon the system-level
design—the heat sink, airow 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 20. This spring force
should not exceed 5.5 pounds of force.