West Control Solutions KS98-1 - Manual (Page 190)

KS98-1 CAN communication features
Every message on the bus activates the KS 98-1 interrupt handler and loads the processor. The message is analyzed
and queued, if the destination of the message is the own address. This queue is handled in the idle task and during the
cyclical system processing phase (at intervals of 100ms).
70% of the CPU capacity is reserved for the engineering. This time is considered as 100 % in the KS98 ET timing dia -
logue. I.e. Min. 30ms are available for general tasks and communication. Included are front and rear instrument inter -
face processing and Profibus handling. However, these loads are insignificant, because, for example, front and rear
interface can only receive one telegram per 100 ms. This means that the CAN communication causes the largest part
of the CPU load.
The PDO handling program is activated, as soon as the processing phase for the engineering within a cycle is finished
(idle-task). Hence, more than 30 % of the processor capacity may be available for CAN communication with small
engineerings. The user can decide freely and at his own responsibility how to use these reserves can.
Receive PDOs
The interrupt handler requires approx. 0,16ms for each PDO.
The event queues comprise 4 x 80 items. There is a queue for all send messages, another one for all PDO receive mes -
sages, still another one for the network receive messages and still another one for the SDO receive messages.
The queues are handled at intervals of 100 ms and during the idle task.
This means that no more than 80 PDOs per 100ms may be received.
The PDO handling is a processor load of approx. 1,2 ms for each individual PDO.
Blockwise handling of 50 receive PDOs takes KS 98-1 18 ms (19 ms, if the same number of PDOs for other receivers
are rejected).
Although the load of the basic communication blocks (C_RM2X, CPREAD, ...) cannot be allocated to a time slot, it is
assigned as a fixed value to the engineering portion automatically.
Send PDOs
The load for transmitted PDOs is nearly the same as for receive PDOs (18ms / 50 PDOs), however, sending is not cycli -
cal.
PDOs are sent only, when a value has changed (threshold adjustable with CSEND, otherwise, there will be a change of
accuracy of the transmitted data format). At the latest after 2 seconds, the values are sent again also if unchanged.
This reduces the output load by an unpredictable percentage. A filter can be used to reduce the transmission frequency
of instable data.
Estimation of CAN bus activities of various instruments
For reducing the data traffic between PMA instruments, PDOs are transmitted only in case of data changes. The
changes are read with the accuracy of the used data format (LSB).
KS800 communication
Both synchronous and asynchronous communication are used for KS800 communication. By configuration, one PDO is
defined as synchronous and one PDO is defined as asynchronous.
A Sync message is sent at intervals of 200ms.
This is followed by reception of a PDO containing the data of one controller channel by each KS800/816 . I.e. refresh-
ing of 8 channels takes 1,6 seconds.
The internal KS800/816 cycle for handling a controller channel is 63,5 ms. If a channel status or correcting variable
change occurs during this cycle time, KS800/81 sends 1 PDO asynchronously.
Description of KS 98-1 CAN bus extension 9499-040-82711
III-190