Instructions

239 C-Control Pro IDE

Less than 125 kbit/s

Up to 1000m

The line lengths are highly dependent on the used cables and the number of participants. It is pos-

sible to use a "twist-pair cables with a characteristic impedance 108-132 Ohm. A maximum of 32

MEGA128CAN units can operate on a bus. It is best to start at the theoretical maximum speed for

the used cable length, and to lower the transfer rate when there is no packet transfer at all or there

occur too many packet errors.

The MEGA128CAN supports the "Base frame format" CAN 2.0A (11 bit identifier) and the extended

frame format "CAN 2.0B (29 bit identifier).

To use the CAN bus in your own projects together with the C-Control Pro Mega128 CAN, it is essen-

tial to understand the CAN data format and the technical details of the CAN bus. Background inform-

ation can be found in books and in Wikipedia: http://en.wikipedia.org/wiki/Controller_Area_Network

Message Objects

The active CAN bus controller works with 15 (MEGA128CAN) or 16 (AVR32Bit) independent mes-

sage objects (MOb) with which one can send and receive messages with certain identifiers. For this

purpose the message objects are parametrized with CAN_SetMOb() for the related task.

Message Objects with a low MOb number have always precedence before a MOb with a higher

number. When two MOb's are capable to receive a certain message, the message will be received

from the MOb with the lower number.

CAN Protocol

The CAN bus controller can simultaneously process normal packets (CAN 2.0A) and extended

packets (CAN 2.0B). CAN bus identifier are passed as 32-bit dword (ULong). Depending on the type

of packets an identifier is 11-bit (V2.0 part A) or 29-bit long (V2.0 part B). The unused bits are ig-

nored. The maskID determines which packages are received for a specific identifier (ID). Only the

bits in the maskID that are "1" are to be reviewed at a bit comparison between the set identifier and

the ID of the incoming packet.

automatic reply

If a Message Object is set to automatic reply, the MOb inherits the Data Length Code (DLC) of the

incoming remote trigger package. I.e. the sender of the trigger packet determines with the DLC the

number of data bytes that are sent in the reply packet.

Message FIFO

During the initialization of the CAN library the user provides RAM for the message FIFO, in which all

incoming CAN packets are stored. The received messages can then be read asynchronously from

the FIFO.