Communications Mode; Using The Transfer Memory - Siemens SIMATIC S5 CP 523 Manual

Technical Description

Communications mode

In Communications mode, message frames of up to 256 bytes in length can be transferred bet-
ween the CPU and a peripheral device connected to the CP 523.
When it receives a "SEND" request from the CPU, the CP 523 transfers the data from the transfer
memory to a Send mailbox. The CP 523 then transfers the data autonomously from the Send
mailbox to the peripheral device.
Data received from the peripheral device is first stored by the CP in a Receive mailbox. On
receiving a "RECEIVE" request from the CPU, the data is forwarded to the transfer where it can be
read out by the CPU.
S5 bus and transfer memory
Data is transferred between the CPU and CP 523 via the S5 bus. Data is stored in an eight-byte
transfer memory in the CP 523. Addresses for the transfer memory are derived from the initial
address of the module and an offset of 0 to 7.
Only when word 0 of the transfer memory has been overwritten with T PW <Initial address of the
module> does the CP 523 read the data from the transfer memory and update the transfer
memory with current values. These current values can then be read by the user program with L PW
statements.
CPU transfers new job
request to word 0 of
the transfer memory
(T PW X).
You can transfer additional information to the CP in words 2, 4 and 6 before the request is sub-
mitted. This depends on the job in question. See the job descriptions for the precise explanation.
Serial interface
The CP 523 has an RS-232-C (V.24) interface and a TTY interface.
The following are examples of peripheral devices that you can connect to the serial interface of
the CP 523:
• Printer with passive or active TTY interface
• Printer with RS-232-C (V.24) interface
• Barcode reader
• Keyboard
• Terminal
• MODEM
• Another CP 523
• CPU 944 (ASCII interface)
• CP 521
• PC
2-2
CP reads out bytes
0 to 7 of the
transfer memory
Figure 2-2. Using the Transfer Memory
CP overwrites bytes
0 to 7 of the transfer
memory with the
current data.
CP 523
CPU can read the
actual data from
the transfer
memory (LPW X).
EWA 4NEB 811 6044-02a