TMPR4956C datasheet(227/286 Pages) TOSHIBA

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Chapter 11 TX4956 System Interface

11-59

Figure 11.3.30 Discarding and Re-executing Processor Single Read Request

11.3.17 Multiple Drivers on the SysAD Bus

In most applications, the SysAD bus is a point-to-point connection between the processor and a

bidirectional, registered transceiver located in an external agent. In this application, the SysAD bus has

two possible drivers: the processor and the external agent.

However, an application may add additional drivers and receivers to the SysAD bus, allowing

transmissions over the SysAD bus that bypass the processor. To accomplish this, the external agent(s)

must coordinate its use of the SysAD bus by using arbitration handshake signals such as EReq* and

PMaster*.

To implement an independent transmission on the SysAD bus that does not involve the processor, the

system executes the following sequence of actions:

The external agent(s) requests the SysAD bus by asserting EReq*.

The processor releases the System interface to slave state.

The external agent(s) allows independent transmission over the SysAD bus, making certain

the EValid* input to the processor is not asserted while the transmission occurs.

When the transmission is complete, the external agent(s) deasserts EReq* to return the

system interface to master state.

To implement multiple drivers, separate Valid lines are required for non-processor chips to

communicate.

EOD

Data

Hi-Z

Addr

Read

SysAD[31:0]

Cycle

MasterClock

SysCmd[4:0]

EValid*

PValid*

EOK*

EReq*

PMaster*

Data

Addr

Hi-Z

TMPR4956C Datasheet(PDF) 227 Page - Toshiba Semiconductor