Commands
201
2-
11
25
Example implementation in the controller
Slave delete bit:
This instruction is executed once when the controller starts up:
D_OUTPUT := NOT D_INPUT
Slave update bit:
The following instruction must be executed once in each PLC cycle:
US_OUTPUT := NOT US_INPUT
(* copy the inverted update bit from the INPUT
telegram to the OUTPUT telegram *)
T1
The PLC will change the delete bit to high (
A
) and leads to the deletion of the FIFO mem-
ory in the control interface.
T2
The control interface will change the delete bit in the input field (
B
) in response to the
event T1 and clears the entire contents of the FIFO memory.
T3
The PLC reflects the inverted state of U
S
-INPUT from the input field in the output field
(
C
). Similarly, the control interface reflects the inverted state of U
M
-OUTPUT in the input
field (
D
). This signals, that both communication partners are ready to receive a telegram.
T4
The PLC transmits an enhanced read command (ER) to IF-OUT (
I
dent
F
rame) (F). At the
same time the PLC takes over U
M
-INPUT to U
M
-OUTPUT (
E
), thus indicating the validity
of a new telegram.
T5
The control interface mirrors the inverted state of U
M
-OUTPUT to U
M
-INTPUT (
G
). This
informs the PLC over the reception of the telegram.
T6
The control interface dealt with the ER and transmits the response to the command into
the input field (
I
). In the same telegram U
S
-OUTPUT is mirrored into U
S
-INTPUT (
H
).
T7
The PLC has received the changed U
S
-INPUT and mirrors the inverted state into U
S
-
OUTPUT (
J
). Only now, the control interface can send another telegram.
T1 T2 T3
T4
T5
T6
T7
D
U
U
IF
OUT
DATA
{
{
IN
DATA
D
U
U
IF
A
B
C
D
E
F
G
J
H
S
M
S
S
M
S
I
Response to ER
Command Enhanced Read (ER)
