Io Data Handling; Input Data Handling - Comtrol DeviceMaster PNIO 2000 Series User Manual

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IO Data Handling

This section describes how the DeviceMaster handles IO data.

When the DeviceMaster receives input data from a serial port, it first converts the

low level serial signals into bytes of raw serial data. Then serial packets are

created from the raw data based on delimiters and/or receiving timer. Packets that

do not have valid delimiters are dropped. Valid packets are put on a receiving

queue, waiting to be sent to IO controller in the next IO update cycle. The

following figure shows the process.

The input data from Ethernet devices are handled similarly. Instead of converting

serial signals, the DeviceMaster receives the input data through a TCP connection

from an Ethernet device. The DeviceMaster manages the connection mode, TCP

port, disconnect mode, etc. Refer to

Configuring an Ethernet Device

on Page 61 for

details regarding Ethernet device configurations. The reset of process is basically

identical between a serial port and an Ethernet device.

At every IO update cycle, the DeviceMaster gets the first packet from the receiving

queue of each serial port and Ethernet device and sends it to IO controller. If the

receiving queue is empty, it retransmits the last packet of that port/device.

Depending on the configuration, an oversize packet could be truncated, dropped,

or saved as record data. The following figure shows how a packet is sent to IO

controller during an IO update cycle.

DeviceMaster PNIO | UP User Guide: 2000639 Rev. A

IO Data Handling - 83

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