Siemens SIMATIC S5 Series, Manual

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Computer Link with 3964(R) Transmission Protocol S5-95U, Second Serial Interface
Character delay time (DT)
This is the maximum permissible time interval between receiving two characters (character delay
time). Only those characters with a delay shorter than the specified time are recognized as valid
characters and transmitted in a frame to the CPU.
In DB1,
”
DT 220
”
is set as default, i.e. the character delay time is 220 ms.
Table 3-7 Character Delay Time Depending on the Transmission Rate in a Computer Link
Transmission Rate
in bit/s
Minimum Adjustable
Character Delay Time
in ms
9600 4800 2400 1200 600 300 200
20 30 50 90 170 310 510
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Priority (PRI)
If both devices make a send request at the same time, the low-priority device postpones its send
request. For data transmission with the 3964(R) transmission protocol, one device must be assigned
high priority (
”
HIGH
”
or
”
H
”
) and the other device low priority (
”
LOW
”
or
”
L
”
).
”
PRI HIGH
”
is in
DB1 the default.
Timeout (TIO)
The maximum time interval that may elapse between transmission of the respective control
characters in a connection buildup and cleardown without an error message being issued. Please
note the following ratios when setting the times:
Character delay time < timeout < block waiting period!
In DB1
”
TIO 2000
”
is the default in DB1, i.e. the timeout is 2000 ms.
Block waiting period (BWT)
Relevant for receiving frames if block check characters (BCC) are used for sending and receiving
(for 3964R).
If the character delay time has been exceeded, the data block that has been sent repeatedly must
arrive at the receiver within the block waiting period. Please note the following ratios when setting
the times: Character delay time < timeout < block waiting period!
In DB1,
”
BWT 4000
”
is the default, i.e. the block waiting period is 4000 ms.
Number of buildup attempts (TTE)
Number of attempts to build up a connection.
In DB1,
”
TTE 6
”
is the default, i.e. after a total of 6 failed attempts, the procedure is aborted and
the connection buildup error is entered in the
”
send
”
coordination byte ( Table 3-1).
Number of send attempts (TTS)
Number of attempts to send data.
In DB1,
”
TTS 6
”
is the default, i.e. after 6 failed attempts to transmit data properly, the send
procedure is aborted.
Reason for discontinuation of the procedure: either parity check error or BCC error ( Table 3-2).
3-14
EWA 4NEB 812 6095-02