Toshiba DeviceNet nv Series, Instruction Manual, Page: 29 / 159

1.5 Basic functions
Unified Controller nv Series type1 light DeviceNet Module DN611B Instruction Manual
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1.5.3
Data update cycle of controller and DN611B
As described in the previous section, the communication function between the DN611B and the slave device
has a poll command / response method and a bit-strobe command / response method. On the other hand,
there are two modes of data exchange between the controller and the module: synchronous mode and
asynchronous mode. DN611B supports asynchronous mode. This section describes the asynchronous mode.
■ Asynchronous mode
Output: The controller writes output data to the slave device in the DN611B, and the DN611B sends the written
output data to the slave device in its own scan cycle regardless of the timing of the controller's output data
writing. As long as the output data from the controller is not updated, the DN611B sends the same data to the
slave device.
Input: The DN611B receives data from slave devices by polling response/bit strobe response. When the
DN611B finishes receiving data from all slave devices, the DN611B updates the input data. The DN611B does
not send a receive completion notice to the controller. The controller reads the input data regardless of the
timing of the DN611B's input data update.
Figure 1-9 Asynchronous mode
There is no timing relationship between the data transfer between the controller and the DN611B and between
the DN611B and the slave device. The transfer between the controller and DN611B is synchronized with the
output and input cycles of the program on the controller. On the other hand, the transfer between the DN611B
and the slave device is synchronized with the scan cycle of DeviceNet.
At this time, data of 1 word (16 bits) is guaranteed.
If the scan cycle of DeviceNet is shorter than the scan cycle of the controller, the time delay of data update
between the controller and slave device will be smaller.
DeviceNet scan time varies depending on the number of slave devices to be connected, the amount of data
transmitted for each slave device, and performance.
Controller
DN611B
Slave devices
Out
Data
Controller data update cycle
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In
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Res Res Res
DN611B Scan