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Communications Mode CP 523

7.6 Sending Message Frames to a Peripheral Device (Job Number A001

)

The CPU can forward up to 256 bytes to the CP 523 with one Send request. This data is referred to

as a message frame in the following.

Schematic for ” sending a message frame"

Figure 7-7. Sending Message Frames to a Peripheral Device

Internal bus

Send message

frame

S5-CPU CP 523

Peripheral

device

Receive

message

frame

8-byte

transfer

memory

Send

mailbox

256 bytes

Serial

interface

Data transfer between the CPU and the CP is always initiated by the CPU with a job request for

"Coordinate data transfer for sending a message frame". When the CP has accepted the send

job, the CPU transfers the message frame in message blocks of eight bytes.

The CP 523 has a Send mailbox of 256 bytes for storing the data from the CPU. The CP 523

accepts data from the transfer memory in the Send mailbox if the CPU has written the

relevant data into word 0 of the transfer memory ( ).

After the CP has received the complete message frame, it transfers the message frame

autonomously from the Send mailbox to the peripheral device via the serial interface ( ).

The CP can only accept another Send request when it has transferred the complete message

frame to the peripheral device.

The following two pages contain a graphic representation of this procedure:

• "Send message frame" flowchart

• Transfer memory assignments from the user program and from the CP 523 for servicing the

Send request

Note:

See 8.1 for a printout and explanation of the statement list of the "SEND" function block. The

function block is a user-friendly interface for handling "Send message frame" requests.

Use of the function block is also explained in 8.1.

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Siemens KS7 Series Specifiche Pagina 165

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