Chapter 8. Signal Descriptions
8-37
MPX Bus Signal ConTguration
State Meaning
AssertedThe MPC7400 has data ready for a pending bus operation
initiated elsewhere in the system (for which the MPC7400 has
previously signaled HIT during the snoop response window), and the
MPC7400 is requesting the data bus in order to service that bus
operation.
NegatedThe MPC7400 is not requesting the data bus to service an
outstanding bus request.
Timing Comments
AssertedDRDY is asserted no earlier than HIT and no earlier than
two cycles before the MPC7400 is able to drive the data (since
DRDY may be followed immediately by DBG and then TA).
NegatedDRDY is negated on the cycle after it is asserted unless
another DRDY is asserted for the next transaction. DRDY may be
fully pipelined on back-to-back cycles when multiple hits are
outstanding.
8.4.6.4 Data Bus Monitor (DMON)Output
The data bus monitor (DMON) signal is strictly optional in the MPX bus protocol.
Following are the state meaning and timing comments for DMON.
State Meaning
AssertedSame as 60x bus interface DBB signal
NegatedSame as 60x bus interface DBB signal
Timing Comments
AssertionSame as 60x bus interface DBB signal
NegationSame as 60x bus interface DBB signal
High ImpedanceSame as 60x bus interface DBB signal
8.4.7 Data Transfer Signals in MPX Bus Mode
The data transfer signals in MPX bus mode transmit data and generate and monitor parity
for the data transfer similarly to that in 60x bus mode, except that they are also used for
data-only transactions. For a detailed description of how the data transfer signals interact in
MPX bus mode, see Section 9.6.2, òData Tenure in MPX Bus Mode.ó
8.4.7.1 Data Bus (DH[0:31], DL[0:31])
The following subsections describe the operation of the data bus signals as inputs and
outputs in MPX bus mode.
8.4.7.1.1 Data Bus (DH[0:31], DL[0:31])Output
Following are the state meaning and timing comments for the DH[0:31], DL[0:31] signals
as outputs in MPX bus mode.