SEND Statement

 

The SEND statement sends byte level IEEE-488 bus data and commands. Commands are sent with the ATN line asserted; whereas data bytes are sent without the ATN line asserted. You specify an I/O Path or an interface select code and a list of messages. The type of message is specified with the keywords CMD, DATA, TALK, LISTEN, SEC, MTA, MLA, UNT, and UNL. For example:

 

 

sends the unlisten command, my listen address, the talk address specified by the value of the variable (Primary), and then the command byte 152.

The CMD message evaluates the following expression values and sends them as command bytes. If the CMD keyword is given with no expressions, it asserts the ATN line. For example:

 

 

The DATA message evaluates the following expression values and sends them as data bytes. If the optional END keyword is added, EOI is set on the last data byte. For example:

 

 

The LISTEN message sends the expression values as listen address commands. The TALK message sends the expression value as a talk address command. The SEC message sends the expression values as secondary address commands. The MLA message sends the interface’s listen address command. The MTA message sends the interface’s talk address command. The UNL message sends the unlisten command and the UNT message sends the untalk command.

 

The computer must be the active controller to use the CMD, TALK, UNT, LISTEN, UNL, SEC, MTA, or MLA messages. Any talk addressed device may send DATA.

The following table lists the bus commands that can be sent with the CMD message.

         

 

Note that the listen and talk address groups (LAG and TAG) consist of 31 different addresses. Each listen and talk address can be further broken down into a secondary address group (SCG). To find the appropriate listen, talk, or secondary address to send for a particular device, use the following equations:

 

Listen Address = Primary Address + 32

Talk Address = Primary Address + 64

Secondary Address = Primary Address + 96

 

The examples below show the high level transfer statement OUTPUT followed by four ways to send the exact same information across the IEEE-488 bus with the SEND statement.