Motorola MPC8260 - Manual (Page 234)

8-2 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part III. The Hardware Interface
8.2 Bus ConÞguration
The 60x bus supports separate bus conÞgurations for internal masters and external bus
masters.
¥ Single-MPC8260 bus mode connects external devices by using only the memory
controller. This is described in Section 8.2.1, ÒSingle MPC8260 Bus Mode.Ó
¥ The 60x-compatible bus mode, described in Section 8.2.2, Ò60x-Compatible Bus
Mode,Ó enables connections to other masters and 60x-bus slaves, such as an external
L2 cache controller.
The Þgures in the following sections show how the MPC8260 can be connected in these
two conÞgurations.
8.2.1 Single MPC8260 Bus Mode
In single-MPC8260 bus mode, the MPC8260 is the only bus device in the system. The
internal memory controller controls all devices on the external pins. Figure 8-1 shows the
signal connections for single-MPC8260 bus mode.
Lane A sub-grouping of signals within a bus. An 8-bit section of the address or data bus may be referred
to as a byte lane for that bus.
Master The device that owns the address or data bus, the device that initiates or requests the transaction.
ModiÞed IdentiÞes a cache block The M state in a MESI or MEI protocol.
Parking Granting potential bus mastership without requiring a bus request from that device. This eliminates
the arbitration delay associated with the bus request.
Pipelining Initiating a bus transaction before the current one Þnishes. This involves running an address tenure
for a new bus transaction before the data tenure for a current bus transaction completes.
Slave The device addressed by the master. The slave is identiÞed in the address tenure and is responsible
for sourcing or sinking the requested data for the master during the data tenure.
Snooping Monitoring addresses driven by a bus master to detect the need for coherency actions.
Split-transaction A transaction with separate request and response tenures.
Tenure The period of bus mastership. For MPC8260, there can be separate address bus tenures and data
bus tenures.
Transaction A complete exchange between two bus devices. A typical transaction is composed of an address
tenure and a data tenure, which may overlap or occur separately from the address tenure. A
transaction can minimally consist of an address tenure alone.
Table 8-1. Terminology (Continued)
Term DeÞnition