Siemens SIMATIC S7-200 System Manual page 102

S7-200 Programmable Controller System Manual
As shown in Table 6-13, 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 6-13 Bytes of the Receive Buffer (SMB86 to SMB94, and SM1B86 to SMB194)
Port 0 Port 1
SMB86 SMB186
SMB87 SMB187
SMB88 SMB188
SMB89 SMB189
SMW90 SMW190
SMW92 SMW192
SMB94 SMB194
88
Description
Receive message MSB
status byte
n: 1 = Receive message function terminated: user issued
disable command.
r: 1 = Receive message function terminated: error in input
parameters or missing start or end condition.
e: 1 = End character received.
t: 1 = Receive message function terminated: timer expired.
c: 1 = Receive message function terminated: maximum
character count achieved.
p 1 = Receive message function terminated: a parity error.
Receive message MSB
control byte
en
en: 0 =Receive message function is disabled.
1 =Receive message function is enabled.
The enable/disable receive message bit is checked each time
the RCV instruction is executed.
sc: 0 =Ignore SMB88 or SMB188.
1 =Use the value of SMB88 or SMB188 to detect start of message.
ec: 0 =Ignore SMB89 or SMB189.
1 =Use the value of SMB89 or SMB189 to detect end of message.
il: 0 =Ignore SMW90 or SMW190.
1 =Use the value of SMW90 or SMW190 to detect an idle line condition.
c/m: 0 =Timer is an inter-character timer.
1 =Timer is a message timer.
tmr: 0 =Ignore SMW92 or SMW192.
1 =Terminate receive if the time period in SMW92 or
SMW192 is exceeded.
bk: 0 =Ignore break conditions.
1 =Use break condition as start of message detection.
Start of message character.
End of message character.
Idle line time period given in milliseconds. The first character received after idle
line time has expired is the start of a new message.
Inter-character/message timer time-out value given in milliseconds. If the time
period is exceeded, the receive message function is terminated.
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.
7
n r e 0 0
7
sc ec il c/m
LSB
0
t c p
LSB
0
tmr bk 0