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PDO Mapping Parameters


A PDO can contain data from several Object Dictionary entries in order to be able to exchange multiple process data variables with one message.

The PDO mapping parameters determine which Object Dictionary entries are contained in a PDO. Single Object Dictionary entries are mapped into a PDO.

The maximum number of data bits available in a PDO is 64. Because the mapping process works on the bit-level a total of 64 Object Dictionary entries can be mapped into a PDO, if each entry is just one bit long. No matter what the length of an individual Object Dictionary entry is, if all the lengths of the mapped entries are added up, the total cannot exceed 64 bits.

A single mapping parameter identifies one specific Object Dictionary entry with its parameters Index, Subindex and length (in bits). These three parameters get coded into one 32-bit value as shown in the table below.

IndexSubindexLenght (bits)
Bits 31 .. 16Bits 15 .. 8Bits 7 .. 0

In the Object Dictionary the Index area from 1600h to 17FFh is reserved for the RPDO mapping parameters, and the area from 1A00h to 1BFFh is reserved for the TPDO mapping parameters. The Index range sizes are the same as used by the PDO communication parameters and directly correlate to each other. For example, the RPDO1 communication parameters are at Index 1400h and the mapping parameters at Index 1600h, the TPDO3 communication parameters are at Index 1802h and the mapping parameters at Index 1A02h.

The following example shows exactly two object links.

These links go from object (process variable) [2345sub67] of the PDO producer to object [5432sub10] of the PDO consumer and from object [6000sub01] of the producer to object [6200sub02] of the consumer. The third transmit object, [2001sub00] is not evaluated on the receiver side and is therefore covered up with a so-called dummy object.