
EM58 • HS58 • HM58 POWERLINK
6.11.2 PDO objects
The real-time data transfer is performed by means of Process Data Objects
(PDO).
PDO communication in POWERLINK is always performed isochronously by PReq
and/or PRes frames. The PRes frames are sent as broadcasts following the
producer/consumer scheme. The PReq frames with unicast addresses comply
with the Master/Slave relationship.
The transmission type of PDO is continuous. There is no “on event” or “on
change” transmission type provided.
6.11.3 PDO Mapping
The PDO Mapping determines the payload of a PDO frame in a POWERLINK
network. PDO payload is transported via the frame types PollRequest and
PollResponse. Due to the IEEE802.3 standard, any Ethernet frame can have a
size between 64 bytes and 1518 bytes. Subtracting the Ethernet- and the
POWERLINK-header possible payload sizes of 36 bytes up to 1490 bytes are
resulting that can be used for PDO data.
The PDO Mapping is derived from the communication relations between the
different nodes in the network. Based on these relations, the payload of the
Transmit PDO frames (TPDOs) and the Receive PDO frames (RPDOs) is defined.
The PDO mapping can be unchangeable ("static mapping") or configurable
("dynamic mapping").
Mapping tables
The PDO Mapping itself is configured in the form of mapping tables in the
Object Dictionary on each node in the network. It consists of PDO
Communication Parameters and PDO Mapping Parameters.
The following regions of the Object Dictionary are assigned for the PDO
Mapping:
Region
Name
Description
1400h - 14FFh PDO_RxCommParam_XXh_REC
Communication
parameters for RPDOs
1600h - 16FFh PDO_RxMappParam_XXh_AU64 Object mapping for RPDOs
1800h - 18FFh PDO_TxCommParam_XXh_REC
see on page 78 and following
Communication
parameters for TPDOs
1A00h - 1AFFh PDO_TxMappParam_XXh_AU64
see on page 79
Object mapping for TPDOs
Relationship of Communication Parameters and Mapping Parameters
A single PDO is always described by a pair of one communication parameter
object and one mapping parameter object. The pairing is based on the lower
byte of the object index.
MAN EM58_HS58_HM58 PL E 1.1.odt
POWERLINK interface
71 of 108