Chapter 8. Signal Descriptions
8-39
Non-Protocol Signal Descriptions
8.4.8.1 Transfer Acknowledge (TA)Input
Following are the state meaning and timing comments for the TA signal.
State Meaning
AssertedSame as 60x bus interface
NegatedSame as 60x bus interface
Timing Comments
AssertionSame as 60x bus interface
NegationSame as 60x bus interface
8.4.8.2 Transfer Error Acknowledge (TEA)
Input
Following are the state meaning and timing comments for the TEA signal.
State Meaning
AssertedThe same as the 60x bus interface except for the comment
about the assertion of TA causing DBB to negate (because the MPX
bus mode does not use DBB, although similar functionality is
provided by the DMON signal in MPX bus mode).
NegatedSame as 60x bus interface
Timing Comments
AssertionMay be asserted on any bus clock cycle during a normal
data tenure, from the cycle following a qualiTed data bus grant to the
cycle of the Tnal TA.
NegationSame as 60x bus interface
8.5 Non-Protocol Signal Descriptions
The following sections describe the signals on the MPC7400 that do not speciTcally
implement the 60x or MPX bus protocols. These signals include the L2 interface signals,
the interrupt and reset signals, processor status and control signals, clock control signals,
and JTAG test signals.
8.5.1 L2 Cache Address/Data
The MPC7400s dedicated L2 cache interface provides all the signals required for the
support of up to 1 Mbyte of synchronous SRAM for data storage. The use of the L2 data
parity (L2DP[0:7]) and L2 low-power mode enable (L2ZZ) signals is optional, and depends
on the SRAMs selected for use with the MPC7400. Note that the least-signiTcant bit of the
L2 address (L2ADDR[17:0]) is identiTed as bit 0, and the most-signiTcant bit is identiTed
as bit 17. See Section 3.7, òL2 Cache Interface,ó for more information on the operation of
the L2 interface and the interactions of these signals.