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2 Simple Application Controllers
The Command String 7
7 - 9
7.3.6 Number of Devices
The Number of Devices is restricted by total number of Communication Bytes. The Transmit/
Receive data message contains a maximum of 250 bytes. Thus, caution must be taken when
reading BIT/WORD data. Refer to the Note below for detailed caution information.
Format B - READ message
Note: Format B cautions
1 ) READ Message - BIT data
The maximum number of BIT devices that can be read at any one time is restricted by the
maximum number of communication bytes (250 bytes) contained in a single message.
Each device is represented by the Device code, Device No, (LB) and Device No. (HB).
(Max No. of Comm. bytes - (Format No. + Stat No. + Command + No. of Devices)) /
(Device code + Device No(LB) + Device No. (HB)) =
(250 - 4) / 3 = 246 / 3 = 82
Therefore, the user can read 1 - 82 BIT devices at any one time.
2 ) READ Message - WORD data
The maximum number of WORD devices that can be read at any one time is restricted by
the maximum number of communication bytes (250 bytes) contained in a single message.
Each device is represented by the Device code, Device No, (LB) and Device No. (HB).
(Max No. of Comm. bytes - (Format No. + Stat No. + Command + No. of Devices)) /
(Device code + Device No(LB) + Device No. (HB)) =
(250 - 4) / 3 = 246 / 3 = 82
Therefore, the user can read 1 - 82 WORD devices at any one time.
Computer
α
2 Controller
02 = +
S
T
X
Command
No. comm
bytes
Format No.
Station No.
Device No.
(HB)
Device code
Device No.
(LB)
Sum check
(HB)
E
T
X
Sum check
(LB)
Device No.
(HB)
Device code
Device No.
(LB)
No. of
devices
02H
(devices)01
*1
01
*1
S
T
X
Complete flag
No. comm
bytes
Format No.
Station No.
or
S
T
X
N
A
K
No. comm
bytes
Format No.
Station No.
Error Code
Station No.
S
T
X
No. comm
bytes
Format No.
Sum check
(HB)
Device status
Sum check
(LB)
Device status
Command
E
T
X
No. of
devices
02H