EM58 • HS58 • HM58 POWERLINK
•
Data (n bytes)
The POWERLINK Basic Frame format is encapsulated by the Ethernet II wrapper
consisting of 14 bytes of leading Ethernet header (Destination and Source MAC
addresses, EtherType) and 4 bytes of terminating CRC32 checksum.
Allowed frame sizes are ranging between 64 bytes to 1518 bytes, thus the
POWERLINK frame can be between 46 bytes and 1500 bytes (see the
NMT_InterfaceGroup_0h_REC.InterfaceMtu_U16
Bit offset
Entry
defined by
Byte offset
7
6
5
4
3
2
1
0
0 … 5
Destination MAC Address
Ethernet
Type II
6 … 11
Source MAC Address
12 … 13
EtherType (0x88AB)
14
res
MessageType
Ethernet
POWERLINK
15
Destination (8 bit node ID)
16
Source (8 bit node ID)
17 … n
Data
n+1 … n+4
CRC32
Ethernet
Type II
POWERLINK is identified via the EtherType 88ABh.
6.7 Message types
6.7.1 Start of Cycle (SoC)
Start of Cycle (SoC, ID = 01h) is a broadcast frame sent by the MN to begin the
POWERLINK cycle (see the “6.8 POWERLINK Cycle” section on page 65). To
maintain a fixed cycle time, the SoC frame is issued on a precise periodic basis,
keeping jitter on it as low as possible; this also serves to the purpose of
providing time synchronisation for all the devices.
6.7.2 PollRequest (PReq)
After the SoC frame has been issued the Isochronous Period is entered (see the
“6.8.1 Isochronous Period” section on page 65). In this key part of the cycle, the
MN polls each CN by means of the PollRequest (PReq, ID = 03h) frame which is
sent only to the selected CN and carry output data for it.
6.7.3 PollResponse (PRes)
Following a PollRequest (PReq) the accessed CN responds to the query by
issuing a PollResponse (PRes, ID = 04h) frame which is instead a multicast frame
carrying input data, made available to all nodes in the network.
MAN EM58_HS58_HM58 PL E 1.1.odt
POWERLINK interface
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