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MELSEC-Q
3 SPECIFICATIONS
3.5 Communication Performance
3.5.1 Scan time
The scan time represents the time to wait for responses from all nodes after the
QJ71DN91 starts sending requests in the polling or bit strobe communication. The
scan time can be calculated using the following expression:
Scan time LS = Σ (TIn + TOn + 0.097) + 0.222
BR + 0.1 (module: ms)
TIn: Transmission time of the reception data from the nth slave. (See the following
expression for details.)
TOn: Transmission time of the transmission data from the nth slave. (See the following
expression for details.)
Σ : Indicates adding values in ( ) of all slave nodes (except for the reserved nodes).
BR: Coefficient corresponding to the baud rate
500kbaud = 1, 250kbaud = 2, 125kbaud = 4
(1) How to calculate TIn
1) When the length of reception data from the nth slave is 8 bytes or less
: TIn=BT + BTa
reception data length (bytes)
2) When the length of reception data from the nth slave is 9 bytes or more
: TIn=(BT + BTa
8 + 0.190) a + {BT + BTa (b+1) + 0.450}
whereas, a = reception data length divided by 7 (round down below
decimal point)
b = remainder of reception data length divided by 7
(2) How to calculate TOn
1) When the length of transmission data to the nth slave is 8 bytes or less
: TOn=BT + BTa
transmission data length (bytes)
2) When the length of transmission data from the nth slave is 9 bytes or more
: TOn=(BT + BTa
8 + 0.130) c + {BT + BTa (d+1) + 1.000}
whereas, c = transmission data length divided by 7 (round down below
decimal point)
d = remainder of transmission data length divided by 7
125 kbaud 250 kbaud 500 kbaud
BT 0.376 0.188 0.094
BTa 0.064 0.032 0.016