AT89C51CC03U-RDTIM datasheet(90/195 Pages) ATMEL

90 / 195 page

AT89C51CC03

4182I–CAN–06/05

fields against the fixed format and the frame size. Errors detected by frame checks

are designated "format errors".

•

ACK Errors

As already mentioned frames received are acknowledged by all receivers through

positive acknowledgement. If no acknowledgement is received by the transmitter of

the message an ACK error is indicated.

Error at Bit Level

•

Monitoring

The ability of the transmitter to detect errors is based on the monitoring of bus

signals. Each node which transmits also observes the bus level and thus detects

differences between the bit sent and the bit received. This permits reliable detection

of global errors and errors local to the transmitter.

•Bit Stuffing

The coding of the individual bits is tested at bit level. The bit representation used by

CAN is "Non Return to Zero (NRZ)" coding, which guarantees maximum efficiency

in bit coding. The synchronization edges are generated by means of bit stuffing.

Error Signalling

If one or more errors are discovered by at least one node using the above mechanisms,

the current transmission is aborted by sending an "error flag". This prevents other nodes

accepting the message and thus ensures the consistency of data throughout the net-

work. After transmission of an erroneous message that has been aborted, the sender

automatically re-attempts transmission.

CAN Controller

Description

The CAN Controller accesses are made through SFR.

Several operations are possible by SFR:

•

arithmetic and logic operations, transfers and program control (SFR is accessible by

direct addressing).

•

15 independent message objects are implemented, a pagination system manages

their accesses.

Any message object can be programmed in a reception buffer block (even non-consec-

utive buffers). For the reception of defined messages one or several receiver message

objects can be masked without participating in the buffer feature. An IT is generated

when the buffer is full. The frames following the buffer-full interrupt will not be taken into

account until at least one of the buffer message objects is re-enabled in reception.

Higher priority of a message object for reception or transmission is given to the lower

message object number.

The programmable 16-bit Timer (CANTIMER) is used to stamp each received and sent

message in the CANSTMP register. This timer starts counting as soon as the CAN con-

troller is enabled by the ENA bit in the CANGCON register.

The Time Trigger Communication (TTC) protocol is supported by the AT89C51CC03.

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