Siemens SIMATIC S7 - SMB2: Freeport Receive Character; SMB3: Freeport Character Error

Special memory (SM) and system symbol names
D.4 SMB2: Freeport receive character
S7-200 SMART
804 System Manual, V2.3, 07/2017, A5E03822230-AF
D.4
SMB2: Freeport receive character
Special memory byte 2 is the Freeport receive character buffer. While in Freeport mode, the
CPU stores each character that the CPU receives in this byte 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 that the CPU receives from Port 0 or Port 1 during
Freeport communication.
Note
Port 0 and Port 1 share SMB2 and SMB3
When the CPU receives a character on Port 0, note the following:
•
The CPU executes the interrupt routine attached to that event (interrupt event 8).
•
SMB2 contains the character received on Port 0.
•
SMB3 contains the parity status of the received character.
Likewise, when the CPU receives a character on Port 1, note the following:
•
The CPU executes the interrupt routine attached to that event (interrupt event 25).
•
SMB2 contains the character received on Port 1.
•
SMB3 contains the parity status of the received character.
D.5
SMB3: Freeport character error
The CPU sets SM3.0 TRUE when Freeport communication detects a parity, framing, break,
or overrun error on a received character. 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 that the CPU received a parity, framing, break, or overrun error
from Port 0 or Port 1:
• FALSE: no error
• TRUE: error