Table 2- 15 X27 (Rs 422/485) Interface (Ascii Driver) - Siemens Simatic S7-300 CP 341 User Manual

Basic Principles of Serial Data Transmission
2.8 Configuration data
X27 (RS 422/485) interface
You will find a description of the parameters for the X27 (RS 422/485) interface in the table
below.
Table 2- 15 X27 (RS 422/485) interface (ASCII driver)
Parameters Description
Operating mode Specifies whether the X27 (RS 422/485)
interface is to be operated in full-duplex
(RS 422) or half-duplex (RS 485) mode.
(See also Serial Transmission of a
Character (Page 29))
Receive line initial state None: This setting only makes sense with
bus-capable special drivers.
R(A) 5V / R(B) 0V: This default setting
supports break detection in "Full-duplex
(RS 422) four-wire mode".
R(A) 0V / R(B) 5V: This default
corresponds to idle state (no senders
active) in "Half-duplex (RS 485) two-wire
mode". Break detection is not possible in
this initial state.
(also see the following figure)
Delete CP receive You can specify whether the CP receive
buffer at startup buffer should be deleted on startup or
existing (old) message frames should be
sent to the CPU.
Only in the case of "Full-Duplex (RS 422) Four-Wire Mode".
1
92
www.gkbpx.com
Range of values
Full-duplex (RS 422)
•
four-wire mode
Half-duplex (RS 485)
•
two-wire mode
None
•
R(A) 5V / R(B) 0V
•
• R(A) 0V / R(B) 5V
• Yes
No
•
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
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Default value
Full-duplex (RS 422)
four-wire mode
R(A) 5V / R(B) 0V
1
1
(In "Half-Duplex
(RS 485) Two-Wire
Mode", the default
setting is R(A) 0V /
R(B) 5V.)
No
Manual, 09/2008, A5E02191071-01