Siemens Simatic S7-200 System Manual page 418

Special Memory (SM) Bits
SMB1: Status Bits
As described in Table D-2, SMB1 contains various potential error indicators. These bits are
set and reset by instructions at execution time.
Table D-2
SM Bits
SM1.0 This bit is turned on by the execution of certain instructions when the result of the
operation is zero.
SM1.1 This bit is turned on by the execution of certain instructions either when an overflow
results or when an illegal numeric value is detected.
SM1.2 This bit is turned on when a negative result is produced by a math operation.
SM1.3 This bit is turned on when division by zero is attempted.
SM1.4 This bit is turned on when the Add to Table instruction attempts to overfill the table.
SM1.5 This bit is turned on when either LIFO or FIFO instructions attempt to read from an
empty table.
SM1.6 This bit is turned on when an attempt to convert a non-BCD value to binary is made.
SM1.7 This bit is turned on when an ASCII value cannot be converted to a valid hexadecimal
value.
SMB2: Freeport Receive Character
SMB2 is the Freeport receive character buffer. As described in Table D-3, each character
received while in Freeport mode is placed in this location for easy access from the ladder
logic program.
Table D-3
SM Byte
SMB2 This byte contains each character that is received from Port 0 or Port 1 during Freeport
communication.
SMB3: Freeport Parity Error
SMB3 is used for Freeport mode and contains a parity error bit that is set when a parity error
is detected on a received character. As shown in Table D-4, SM3.0 turns on when a parity
error is detected. Use this bit to discard the message.
Table D-4
SM Bits
SM3.0 Parity error from Port 0 or Port 1 (0 = no error; 1 = error was detected)
SM3.1 to
Reserved
SM3.7
D-2
Special Memory Byte SMB1 (SM1.0 to SM1.7)
Special Memory Byte SMB2
Special Memory Byte SMB3 (SM3.0 to SM3.7)
Description
Description
Description
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02