Siemens Simatic S7 Series

Special memory (SM) and system symbol names
D.4 SMB2: Freeport receive character
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
669
D.4
SMB2: Freeport receive character
Special memory byte 2 is the Freeport receive character buffer. Each character that is
received while in Freeport mode is placed in this location for easy access by your program.
Table D- 3 SMB2 Freeport received character
S7-200 SMART
symbol name
SM address
Description
Receive_Char SMB2 This byte contains each character received from Port 0 or Port 1 during Freeport com-
munication.
Note
SMB2 and SMB3 are shared between port 0 and port 1
When the reception of a character on port 0 results in the execution of the interrupt routine
attached to that event (interrupt event 8), SMB2 contains the character received on
port 0,
and SMB3 contains the parity status of that character.
When the reception of a character on port 1 results in the execution of the interrupt routine
attached to that event (interrupt event 25), SMB2 contains the character received on port 1,
and SM
B3 contains the error status of that character.
D.5
SMB3: Freeport character error
SMB3 is used for Freeport mode and contains an error bit that is set when a parity, framing,
break, or overrun error is detected on a received character. SM3.0 is set ON when a parity,
framing, break, or overrun error is detected. Use this bit to discard the message.
Table D- 4 SMB3 Freeport character error
S7-200 SMART
symbol name
SM address
Description
Parity_Err SM3.0 This bit indicates a parity, framing, break, or overrun error received from Port 0 or
Port 1. (0=no error; 1=error)