TMPR4955AF datasheet(98/168 Pages) TOSHIBA

98 / 168 page

Chapter 6 TX4955A System Interface

6-26

6.2.11

System Interface Command and Data Identifiers

System interface commands specify the type of system interface and its properties. This

specification is performed in the request address cycle.

The system interface data

identifiers specify the properties of the data transferred during the system interface data

cycle.

Of the system interface commands and data identifiers used for external requests, set

the bits and fields that are reserved to “1.” In the case of system interface commands and

data identifiers used for processor requests, bits, field contents and data identifiers that are

reserved in the commands are undefined.

6.2.11.1 Syntax of commands and data identifiers

System interface commands and data identifiers consist of 9 bits. These commands are

sent by the SysCmd bus from the processor to the external agent or from the external agent

to the processor during either the address cycle or the data cycle. Bit 8 (MSB) of the

SysCmd bus specifies whether the SysCmd contents at that time are a command or a data

identifier (namely, whether the current cycle is an address cycle or a data cycle). If the

contents are a system interface command, then SysCmd(8) must be set to “0.” If the

contents are a system interface data identifier, then SysCmd(8) must be set to “1.”

6.2.11.2 Syntax of system interface commands

Following is an explanation of the SysCmd bus structure in the case of a system interface

command. Figure 6.2.24 illustrates the structure common to all system interface

commands.

Request type

Request specific

Figure 6.2.24 Syntax Bit Structure of System Interface Command

SysCmd(8) must always be set to “0” in the case of system interface commands.

SysCmd(7:5) specifies the type of system interface request (read, write, null). Table

6.2.7 indicates the SysCmd(7:5) specification method.

Table 6.2.7 SysCmd(7:5) Specification Method for System Interface Commands

SysCmd(7:5)

Command

Read request

Reserve

Write request

Null request

∼ 7

Reserve

SysCmd(4:0) varies depending on the type of request. Each specification type is

indicated below.

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