Toshiba S20LP - Manual (Page 13)

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2. Scan transmission overview
The Scan transmission method is suitable for real time control data linkage.
In the S20LP, data sending station is rotated cyclically. Each station has common memory for
Scan transmission. The size of the common memory is 4096 words. When a station becomes the
data sender station, it sends data of prespecified area of the common memory. All other stations
receive the data, and store them into their common memory. Therefore, the common memory in
each station is totally updated in a transmission cycle.
The common memory is allocated to the Link register (W) in the T2N/T3H. The size of the link
register is 2048 words. The link register is a part of common memory. By simply reading/writing
data from/to the Link registers, high speed data linkage is achieved.
S20LP
T2N’s Link
register
(3)
Receive
(2)
Receive
(1)
Send
Common
memory
Read
Write
STN T2N
T2N’s Link
register
(3)
Receive
(2)
Send
(1)
Receive
Common
memory
Read
Read
Write
STN T2N
T3H’s Link
register
(3)
Send
(2)
Receive
(1)
Receive
Common
memory
Read
Write
STN T3H
Note 1) The data send block(s) of each station is prespecified by using the S-LS.
Note 2) Data transfer between common memory and Link registers is executed by T2N/T3H's
OS. The transfer direction (read or write) is automatically decided.