Communications Mode
CP 523
7.6
Sending Message Frames to a Peripheral Device (Job Number A001
H
)
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
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
a a
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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7-60
EWA 4NEB 811 6044-02a