Siemens Simatic S7-200 System Manual page 428

Special Memory (SM) Bits
SMB92 SMB192
SMB93 SMB193
SMB94 SMB194
SMB110 to SMB115: DP Standard Protocol Status
As described in Table D-17, SMB110 through SMB115 are used to monitor the status of the
DP standard portocol.
Note
These locations are for status only. Do not write to them. The locations show values set by
the DP master device during the configuration process.
Table D-17
SM Byte
SMB110
SMB111 This byte defines the address of the slave's master (0 to 126).
SMB112 These bytes define the V memory address of the output buffer (offset from VB0).
SMB113
SM112 is the most significant byte, and SM113 is the least significant byte.
SMB114 This byte defines the number of bytes for the output data.
SMB115 This byte defines the number of bytes for the input data.
D-12
Inter-character/message timer time-out value (in milliseconds). If the time
period is exceeded, the receive message is terminated.
SM92 (or SM192) is the most significant byte, and SM93 (or SM193) is the
least significant byte.
Maximum number of characters to be received (1 to 255 bytes).
Note: This range must be set to the expected maximum buffer size, even if
the character count message termination is not used.
Special Memory Bytes SMB110 to SMB115
MSB LSB
7 0
0 0 0 0 0 0 s s
ss: DP standard status byte
00 = DP communications have not been initiated since power on
01 = Configuration/parameter assignment error detected
10 = Currently in data exchange mode
11 = Dropped out of data exchange mode
SM111 to SM115 are updated each time the CPU accepts configuration-parameter
assignment information. These locations are updated even if a configuration-
parameter assignment error is detected. These locations are cleared every time the
CPU is turned on.
Description
Port 1: DP standard protocol status byte
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02