P82C150AHT datasheet(20/36 Pages) PHILIPS

20 / 36 page

1996 Jun 19

Philips Semiconductors

Preliminary speciﬁcation

CAN Serial Linked I/O device (SLIO) with

digital and analog port functions

P82C150

7.4

Initialization

7.4.1

IDENTIFIER PROGRAMMING

Most of the P82C150 identifier bits are fixed. Four bits are

programmable via port pins P3 to P0. All output drivers are

disabled at reset, also P3 to P0. Thus the outputs are

floating unless the input level is defined by external

components to define identifier bits. They are latched at

the end of reset, and P3 to P0 can be used as port pins.

It is not allowed, according to the CAN protocol

specification, that multiple bus nodes transmit the same

identifier bit combination. Therefore a P82C150 must have

one of the 16 possible identifier bit combinations, one that

is not yet occupied.

7.4.2

RESET FUNCTION

RST = HIGH disables all output drivers P16 to P0, TX0

and TX1. All I/O Registers are automatically cleared and

set to logic 0. The bit time is set greater than 50

µs.

If a particular clock period is necessary, e.g. for a

dedicated DPM output frequency, this can be achieved by

feeding an external clock signal into P0. RST and TEST

must be permanently HIGH for this special mode. A reset

is then performed as usual (RST = HIGH; TEST = LOW).

Table 14 Situation after RESET

7.4.3

BIT TIME CALIBRATION

The P82C150 must receive at least three messages to

calibrate its bit time after reset or change of bus mode.

The first message is used to detect the bit time length

(rough calibration) between two consecutive falling edges

at the output of the CAN input comparator. Therefore the

bit stream should contain a sequence of ‘1010’.

STATUS BITS

IDENTIFIER BITS

RSTD = 1

ID.8 equals P3

EW = 1

ID.5 equals P2

BM1 = 0

ID.4 equals P1

BM0 = 0

ID.3 equals P0

After rough calibration the P82C150 can receive any valid

CAN message correctly and executes respective

commands without giving an acknowledge. With another

valid CAN message and additionally with one valid

calibration message the P82C150 is fully calibrated and

sends its ‘sign-on’ message. As long as the P82C150 is

fully calibrated the P82C150 acts as an active CAN node.

The P82C150 treats any CAN message (including the

calibration message) as a valid message, when these

messages are terminated by an error passive frame

because of a missing acknowledge. This situation may

occur whenever a host node works together with

P82C150’s and the host node doesn’t receive an

acknowledge as long as the P82C150’s are not fully

calibrated.

7.4.3.1

Sign-on message

This special Data Frame is transmitted once by the

P82C150 after entering the calibrated state. It indicates to

the host node that the P82C150 is ready for transmission.

The sign-on message returns the contents of the Data

Input Register, and can be recognized by the host mode by

checking the RSTD status bit:

• Sign-on message RSTD = 1

• Other Data Frames RSTD = 0

Note that in the sign-on message the EW bit is logic 1.

Nevertheless the P82C150 status with the error counters

are set to logic 0.

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