MIPS R4000 Microprocessor User's Manual 295
System Interface
Interface Buses
Figure 12-1 shows the primary communication paths for the System
interface: a 64-bit address and data bus, SysAD(63:0), and a 9-bit
command bus, SysCmd(8:0). These SysAD and the SysCmd buses are
bidirectional; that is, they are driven by the processor to issue a processor
request, and by the external agent to issue an external request (see
Processor and External Requests, in this chapter, for more information).
A request through the System interface consists of:
• an address
• a System interface command that specifies the precise nature of
the request
• a series of data elements if the request is for a write, read
response, or update.
Figure 12-1 System Interface Buses
R4000
External Agent
SysAD(63:0)
SysCmd(8:0)
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