TMPR4955AF datasheet(129/168 Pages) TOSHIBA

129 / 168 page

Chapter 6 TX4955A System Interface

6-57

EOD

Data

Hi-Z

Addr

Read

611

SysAD(31:0)

SCycle

SClock

SysCmd(4:0)

EValid*

PValid*

EOK*

EReq*

PMaster*

Data

Addr

Hi-Z

Figure 6.3.31 Discarding and Re-executing Processor Single Read Request

6.3.17

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

EReq

EReq* and PMaster

PMaster

PMaster*.

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

processor, the system executes the following sequence of actions:

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

EReq

EReq*.

2. The processor releases the System interface to slave state.

3. The external agent(s) allows independent transmission over the SysAD bus,

making certain the EValid

EValid

EValid* input to the processor is not asserted while the

transmission occurs.

4. When the transmission is complete, the external agent(s) deasserts EReq

EReq

EReq* to

return the system interface to master state.

To implement multiple drivers, separate Valid

Valid

Valid lines are required for non-processor chips

to communicate.

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