Managing Flow Control - Siemens SIMATIC S7 System Manual
Hide thumbs
Also See for SIMATIC S7:
- System manual (866 pages) ,
- Functional safety manual (212 pages) ,
- User manual (134 pages)
Table of Contents
Advertisement
105BCommunication processor
12.3 Point-to-Point (PtP) communication
The STEP 7 user program can also configure the port or change the existing configuration
with the PORT_CFG instruction (Page 534).
Note
Parameter values set from the PORT_CFG instruction in the user program override port
configuration settings set from the device configuration. Note that the S7-1200 does not
retain parameters set from the PORT_CFG instruction in the event of power down.
Parameter
Baud rate
Parity
Number of stop bits
Flow control
Wait time
12.3.2.1
Managing flow control
Flow control refers to a mechanism for balancing the sending and receiving of data
transmissions so that no data is lost. Flow control ensures that a transmitting device is not
sending more information than a receiving device can handle. Flow control can be
accomplished through either hardware or software. The RS232 CM supports both hardware
and software flow control. The RS485 CM and CB do not support flow control. You specify
the type of flow control either when you configure the port (Page 549) or with the
PORT_CFG instruction (Page 534).
Hardware flow control works through the Request-to-send (RTS) and Clear-to-send (CTS)
communication signals. With the RS232 CM, the RTS signal is output from pin 7 and the
CTS signal is received through pin 8. The RS232 CM is a DTE (Data Terminal Equipment)
device which asserts RTS as an output and monitors CTS as an input.
550
Definition
The default value for the baud rate is 9.6 Kbits per second. Valid choices are: 300 baud,
600 baud, 1.2 Kbits, 2.4 Kbits, 4.8 Kbits, 9.6 Kbits, 19.2 Kbits, 38.4 Kbits, 57.6 Kbits, 76.8
Kbits, and 115.2 Kbits.
The default value for parity is no parity. Valid choices are: No parity, even, odd, mark (parity
bit always set to 1), and space (parity bit always set to 0).
The number of stop bits can be either one or two. The default is one.
For the RS232 communication module, you can select either hardware or software flow
control, as described in the section "Managing flow control (Page 550)". If you select
hardware flow control, you can select whether the RTS signal is always on, or RTS is
switched. If you select software flow control, you can define the XON and XOFF characters.
The RS485 communication interfaces do not support flow control.
Wait time specifies the time that the CM or CB waits to receive CTS after asserting RTS, or
for receiving an XON after receiving an XOFF, depending on the type of flow control. If the
wait time expires before the communication interface receives an expected CTS or XON,
the CM or CB aborts the transmit operation and returns an error to the user program. You
specify the wait time in milliseconds. The range is 0 to 65535 milliseconds.
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
- Quick Links:
- Introducing the S7-1200 Plc
Hide quick links:
Advertisement
Table of Contents
