TMPR4955F datasheet(74/168 Pages) TOSHIBA

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Chapter 6 TX4955A System Interface

6-2

6.2.1

Interface bus

Figure 6.2.1 illustrates the 32-bit address/data bus SysAD (31:0), which is the main

communication bus of the system interface, and the 9-bit command bus SysCmd (8:0).

SysAD and SysCmd are bi-directional busses. In other words, these two busses are used for

the processor to issue processor requests and for the external agent to issue external

requests.

Figure 6.2.1 System Interface Bus

Requests sent via the system interface consist of the following:

•

Address

•

System interface command that strictly specifies the type of request

•

Series of data elements for when the request is a particular write or read process.

6.2.2

Address cycle and data cycle

Cycles during which valid addresses exist on the SysAD bus are referred to as address

cycles. Also, cycles during which valid data exist on the SysAD bus are referred to as data

cycles. Validity is determined depending on the ValidIn signals and ValidOut signals.

The SysCmd bus is used to identify the contents of the SysAD bus for all cycles at which

it is to be valid. The most significant bit of the SysCmd bus is used to indicate whether the

current cycle is an address cycle or a data cycle.

•

In the case of an address cycle [SysCmd(8) = 0], the remaining bits SysCmd(7:0) of

the SysCmd bus contain the system interface commands.

•

In the case of a data cycle [SysCmd(8) = 1], the remaining bits SysCmd(7:0) of the

SysCmd bus contain the data identifier.

SysCmd (8:0)

SysAD (31:0)

TX4955A

External agent

TMPR4955F Datasheet(PDF) 74 Page - Toshiba Semiconductor