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model 2000 DeviceNet Module Manual (DN611/DN611A)
Chapter 4 Operating Procedures for the DN611 (Software)
4
(4) Local node parameter (PARA_LOCAL)
PARA_LOCAL structure
PORT WORD type Port No.
LOCAL_ADR WORD type Local node address
POL_TRMODE WORD type Polling transmission mode
SCAN_INTERVAL WORD type Scan interval waiting time
BGPOL_RATIO WORD type Background poll ratio
RETR_CNT WORD type Retransmission counter
TR_TIMING WORD type Transmission timing
(5) Supplementary note on polling transmission mode
If a polling slave device returns no response in polling transmission mode, the DN611
may take different approaches to the problem.
(a) Polling transmission mode = 0
• The master device makes a polling request asynchronous with the response
of a slave device in polling mode, and waits for polling response from it for 20
ms after making the request.
After the 20 ms of waiting for its response, the DN611 starts the next scan.
• As long as there is a slave device which does not respond, the master device
waits 20 ms for response every scan.
• The real scan cycle in cases where there is a slave device which does not
respond is expressed as follows:
Real scan cycle = Real scan cycle in normal operation + 20 ms
Table 4-13 Local Node Parameters
Parameter Description
Port No. Set 0 fixed.
Local node address The same address as set with the rotary switches
Polling transmitting
mode
0: A polling request is made to all slave devices, followed by waiting for
batch polling response.
1: Polling response is waited for after requesting polling to each slave
device.
Scan interval wait time Specify a wait time for the next access to start after completing access
to all slave devices.
Minimum: 2 ms Maximum: 10,000 ms
Background poll ratio Devices for which background polling is specified (set with slave
parameters) are accessed at the scan interval set in poll ratio.
Example: If 5 is set, access is made every 5 scans. This parameter is
effective for both polling mode devices and bit strobe mode devices.
Retransmission counter Set 1 fixed.
Transmission timing A value for slave devices to detect transmission timeout if the DN611
doesn't access for a certain interval or more. Set a value greater than
the scan cycle of 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 longer than the
transmission interval of the user program must be specified.
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