1996 Jun 19

19

Philips Semiconductors

Preliminary specification

CAN Serial Linked I/O device (SLIO) with

digital and analog port functions

P82C150

7.3.7

The transmit and receive logic stores the destuffed bit

stream which was received or is about to be transmitted.

The incoming Identifier is compared with that of the

P82C150. The content of the message is transferred to the

port logic in case of matching.

At transmission, the message about to be sent is put

together: the Identifier, the status information, the register

address and the content of the addressed register from the

port logic.

7.3.8

The Bit Stream Processor (BSP) is a sequencer to control

the data stream between the transmit/receive logic

(parallel data) and the on-chip CAN transceiver (serial

data). Reception/transmission, bit stuffing/destuffing,

arbitration and error detection, according to CAN protocol

specification version 2.0 A and B (passive), are performed.

Further, automatic re-transmission of corrupted messages

is handled by means of continuously comparing the output

bit stream with the input bit stream. Moreover, the Bit

Stream Processor provides control information to calibrate

the internal bit time.

The Error Management Logic is responsible for the

complete CAN-inherent error management.

7.3.9

The P82C150 contains an on-chip RC-oscillator. The bit

time is automatically calibrated by messages being

received via CAN-bus. During start-up (after wake-up or

reset) any message is used to calibrate the bit time until

the calibration is sufficient to receive messages correctly.

From this time on, the bit time is calibrated and fine-tuned

by calibration messages with a special Identifier

transmitted by the crystal-controlled host.

Only P82C150 nodes being calibrated by calibration

messages can transmit messages. The first message is

transmitted directly after entering the calibrated state

(‘sign-on’ message). Since the P82C150 is not able to

transmit as long as the bit time is not calibrated, it cannot

wake-up other CAN nodes via the bus line. Hence to keep

the network alive, the calibration message must be

transmitted regularly by a crystal-controlled (host) node

with a maximum repetition period of 8192 bit (bit length

measured by the 82C150). It is recommended to select a

repetition period between 3800 and maximum 8000 bit

times.

7.3.10

The calibration message has to meet the following

requirements

• Transmitted by a crystal-controlled node (host node)

• Identifier: 000 1010 1010 (1 = recessive; 0 = dominant)

• RTR bit: 0

• Allowed control field: DLC=2to8

• The first recessive to dominant transition after the

control field must be followed by another recessive to

dominant transition in a distance of exactly 32 bit (stuff

bits included).

Example of a suitable calibration message (there are

others using different data bytes; see Table 13):

• Data length code: 0010

• 1st data byte: 1010 1010 (AAH)

• 2nd data byte: 0000 0100 (04H).

Table 13 Example of a suitable calibration message

The two important 1/0 transitions are marked by underlines; see note 1.

Note

1. I = stuff bit (recessive); the total length is 67 bit from start-of-frame to end-of-intermission.

SOF

ARBITRATION FIELD

CONTROL

FIELD

DATA BYTE 1

DATA BYTE 2

CRC FIELD

0

000 1010 1010 0

000I010

1010 1010

0000I 0100

000I0 1011 1000 00I0