Controller Area Networks for Embedded Systems - Networked Embedded Systems - page 380

In the same way, a number of default PDOs are defined, together with a default mapping:

• RPDO

:Uptodigitaloutputscanbereceivedfromthenetwork
through this RPDO that are actuated immediately.
• TPDO

( digital outputs )

: Up to  digital inputs can be sent over the network through this
TPDO, according to an event-drive scheme. his means, the PDO is transmitted as soon
as one digital input changes its value (provided it is not masked off via the interrupt mask).
• RPDO

( digital inputs )

: Up to  analogue outputs—each one encoded on  bits—can
be received from the network through this RPDO.
• TPDO

( analogue outputs )

: Up to  analogue inputs—each one encoded on  bits—can
be sent on the network through this TPDO, according to an event-drive scheme.

( analogue inputs )

OnlyPDOsconcerningthesupportedfunctionalitieshavetobeprovidedefectively.However,
additional manufacturer-specific PDOs could be included in the module.

15.7.2 Device Behavior
In the profile specification, also the behavior of devices is defined in a formal way. In the case
of generic I/O modules, block diagrams are provided that describe how information is exchanged
betweentheCANopennetworkandtherealworldandthewaysuchoperationscanbeconigured.

15.7.2.1 Digital Input Devices
In Figure . the sequence of steps involved in the processing chain of a digital input is shows. Details
on the way each operation is carried out can be changed by configuring the appropriate entries of the
OD. A filter constant can be activated separately () on each single digital input channel () by means
of object  h ; moreover, its polarity can be optionally changed () through object  h .hen,
all bits associated to the different input channels are stored in the suitable entries of the OD (object
 h ), from where they will be subsequently extracted and sent over the network (). In this case,
valuesareirstmappedontothepayloadofaPDOthroughthePDOmappingmechanism();then
the correct identifier is selected () by means of the PDO communication parameter.

Default
mapping
parameter

Default
communication
parameter

Filter
constant

1

Optional
filter

1A00 h 6003 h

1800 h

Digital input
(single)

3 5 6 7

4

Entry
into
6000 h

Change
polarity

Transmit
TPDO1

MAP
into TPDO1

Transmission
over CAN

2

6002 h 6006 h

Any change

Polarity
input

6007 h

TX
Trigger

OR

High to low

6008 h Interrupt

enable

6005 h

Low to high

FIGURE . Conceptual architecture of digital inputs.