Siemens Simatic S7-200 System Manual page 93

As shown in Table 6-12, the Receive instruction allows you to select the message start and message end
conditions, using SMB86 through SMB94 for port 0 and SMB186 through SMB194 for port 1.
Tip
The receive message function is automatically terminated in case of an overrun or a parity error. You
must define a start condition and an end condition (maximum character count) for the receive message
function to operate.
Table 6-12 Bytes of the Receive Buffer (SMB86 to SMB94, and SM1B86 to SMB194)
Port 0 Port 1 Description
SMB86 SMB186 Receive message status byte
n:
r:
e:
t:
c:
p
SMB87 SMB187 Receive message control byte
en: 0 =Receive message function is disabled.
sc: 0 =Ignore SMB88 or SMB188.
ec: 0 =Ignore SMB89 or SMB189.
il:
c/m: 0 =Timer is an inter-character timer.
tmr: 0 =Ignore SMW92 or SMW192.
bk: 0 =Ignore break conditions.
SMB88 SMB188 Start of message character.
SMB89 SMB189 End of message character.
SMW90 SMW190 Idle line time period given in milliseconds. The first character received after idle line time
has expired is the start of a new message.
SMW92 SMW192 Inter-character/message timer time-out value given in milliseconds. If the time period is
exceeded, the receive message function is terminated.
SMB94 SMB194 Maximum number of characters to be received (1 to 255 bytes). This range must be set to
the expected maximum buffer size, even if the character count message termination is not
used.
1 = Receive message function terminated: user issued disable command.
1 = Receive message function terminated: error in input parameters
or missing start or end condition.
1 = End character received.
1 = Receive message function terminated: timer expired.
1 = Receive message function terminated: maximum character count achieved.
1 = Receive message function terminated: a parity error.
1 =Receive message function is enabled.
The enable/disable receive message bit is checked each time
the RCV instruction is executed.
1 =Use the value of SMB88 or SMB188 to detect start of message.
1 =Use the value of SMB89 or SMB189 to detect end of message.
0 =Ignore SMW90 or SMW190.
1 =Use the value of SMW90 or SMW190 to detect an idle line condition.
1 =Timer is a message timer.
1 =Terminate receive if the time period in SMW92 or SMW192 is exceeded.
1 =Use break condition as start of message detection.
S7-200 Instruction Set
MSB
7
n r e 0 0
MSB
7
en sc ec il c/m
Chapter 6
LSB
0
t c p
6
LSB
0
tmr bk 0
81