DeviceNet Interface Notes DeviceNet Protocol supports Master/Slave, Multiple Master and Peer to Peer Communications. 1771-SDN Scanner for 1771 platform, 1747-SDN for SLC-500 platform, 1756-DNB for the ControlLogix platform, and 1784-PCIDS for the PC platforms are currently available Network Masters. Network Masters send outputs from the platform to each slave device and receive inputs from each slave device to be put to the platform. User program in PLC or PC utilizes data in platform to do actual control of devices over DeviceNet.
Producer/Consumer Data is identified as to it's content –No more Source/Destination requirements –No sense of mastership Allows the functionality of the Source/Destination models: Master/Slave and Peer-to-Peer Additional models allowed because relationships can be built dynamically: –Multicast - one to many, many to one –Change of State, event based; Cyclic, time based Superior performance because bandwidth is not wasted Examples - DeviceNet, ControlNet, FIP, Fieldbus
PLC I/O 1I/O 2I/O 3 1,4,... 2,5,.. 3,6,.. Network Models - Master/Slave The simplest and most understood; “polling” The PLC or scanner is the master and I/O devices are the slaves – The slaves speak only when spoken to – Only one master per slave (“single master”) – Deterministic but not repeatable Network examples - Remote I/O, Profibus DP, Interbus- S, Seriplex, LON
Protocol Notes DeviceNet protocol supports both Polled and Strobed commands and responses. Strobe Command/Response -- Strobe Command - An 8 byte I/O message broadcast to all Slaves on network at same time. 1 bit of output data for each possible node number. 8 byte message looks like 64 bit bitmask with node number of device acting as index into bitmask to extract devices 1 bit of data. 0 7 8 15 Byte 0 Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 24 31 16 23 39 32 47 48 55 56 63 40 Strobe Transmission format Node/Bit #
Protocol Notes ( Cont ) -- Strobe Response - All Strobe Slave devices will send back their input data, if a slave is also an input device. Poll Command/Response -- Poll Command - An I/O message is directed towards a single, specific Slave ( point-to-point ). The Master must transmit a separate Poll Command for each one of its Slaves that is to be polled. -- Poll Response - Polled Slave device will send back its input data, if slave is also an input device.
... (up to 63) Strobe/responsesPolls/Responses...... (up to 63)..... P1 R1 P2 R2 ISD S S..........packet processing time........ New Cycle..... P R Scan Cycle STROBE: This multicast message starts off the scan cycle. Strobe-able slaves respond based on their latency. POLL: Sent out even as strobe responses are being received, as bandwidth allows. INTER SCAN DELAY: User selectable minimum quiet time to allow other devices access to the network. Scanner will not start another scan cycle (even if packet processing is complete).
PLC I/O 1I/O 2I/O 3 #2 #1 #3 Network Models - Change of State Devices report data (input or output) on a change-of- state basis as the events happen –Rather than a master going through a polling list (scanning), Change of State is more efficient for discrete applications – Network traffic is significantly reduced – Performance is greatly improved Background heartbeat for device health Can be used in Master/Slave, Peer-to-Peer, or Multimaster environments
PLC I/O 1I/O 2I/O 3 every 500 ms every 2000 ms every 25 ms Network Models - Cyclic Data Production Devices report data on a user-configured time increment basis (input or output) Cyclic Data Production is more efficient for applications with slowly changing I/O (analog) – Network traffic is reduced – Performance is repeatable Can be used in Master/Slave, Peer-to-Peer, or Multimaster environments
DeviceNet COS/Cyclic COS / Cyclic Scan Model –Network bandwidth and CPU load both reduced dramatically from Poll/Strobe scheme –Note: Hybrid systems are allowed (any mix of COS, Cyclic, Poll/Strobe) Co 6 Co 1 Cy 2 Cy 2....... Change....... S R3R3 P4P4 P2P2 P1P1 R1R1 R2R2 P3P3 P5P5 R4R4 R5R5 P6P6 R6R6 S COS / Cyclic Model Poll / Strobe Model ISDISD
Network Models Multimaster I/O 1 PLC1 MMI PLC2 DRIVE 1 DRIVE 2 DRIVE 3 PLC 1 “owns” Drive 1, Drive 2 and Drive 3. PLC2 “owns” I/O 1 and MMI. A device can only be owned by 1 master on the network.
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