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Table 4.14 Local Station Parameters (2/2)
Parameter Description
Transmission timing
Is the value for slave devices to detect transmission timeout when the
DN211 doesn't access for a certain interval or more.
Set a value larger than the scan cycle to slave devices(usually, 100 ms
or more).
• When a slave device with background polling is installed, set a value of
time longer than (scan cycle x poll ratio).
• For synchronous mode communication, an interval time value
longer than the transmission interval of the user program must be
specified.
d) Supplement to the Polling Transmission Mode
The DN211 resolution varies when a slave device in polling mode results in no response after
selecting the polling transmission mode.
When the polling transmission mode = 0
• The master device performs polling requests asynchronously with the responses of slave
devices in polling mode; the master device waits for the polling response from a slave device
for 20 ms after executing a request. When the 20 ms exceeds, the next scan starts.
• As long as a no-responding slave device is found, the master device performs 20 ms of
response wait time per scan.
• The real scan cycle, when a no-responding slave device is found, is expressed in the
following formula:
Real scan cycle = Real scan cycle in normal operation + 20 ms
When the polling transmission mode = 1
• The master device checks for the response from a slave device in polling mode and
sequentially executes polling requests to individual slave devices. When polling results in no
response from a slave device, the master device waits for 20 ms before executing a polling
request to the next slave device.
• When three consecutive timeouts occur for a no-responding slave device, the slave device is
delisted from the scan list in the DN211. This will allow the DN211 to transmit with the
remaining slave devices in normal operation, and no wait time for response takes place.
• Only the slave devices which have three consecutive timeouts of no response will be delisted
from the scan list. When a slave device has two consecutive timeouts of no response but
responds to the third polling, the number of timeouts of no response is cleared.
• The DN211 periodically checks for the response from the slave devices delisted from the
scan list; if a delisted slave device responds, the device is re-registered in the scan list.
• When n units of slave devices results in no response at the same time, the real scan cycle for
three consecutive timeouts is expressed in the following formula.
Real scan cycle = Real scan cycle in normal operation + n units x 20 ms