ST72F521R9TC View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST72F521R9TC

8-BIT MCU WITH NESTED INTERRUPTS, FLASH, 10-BIT ADC, FIVE TIMERS, SPI, SCI, I2C, CAN INTERFACE

STMicroelectronics 

ST72521

CONTROLLER AREA NETWORK (Cont’d)

10.8.5 List of CAN Cell Limitations

10.8.5.1 Omitted SOF bit

Symptom:

Start of Frame (SOF) bit is omitted if transmission

is requested in the last Intermission bit.

Test Case:

5.3.1 10-Kbit Stress Test

Details:

The IUT is requested to start transmission immedi-

ately after the completion of the previous transmis-

sion. The LT also starts its transmission and as-

serts the SOF bit just after the 3rd Intermission bit.

The IUT also starts transmission but omits the

SOF bit. The IUT wins the arbitration and contin-

ues the transmission. The frame is sent correctly.

Impact On The Application:

As this effect only occurs when the IUT detects a

SOF bit on the CAN bus, the fact that it omits its

own SOF bit has no impact on the communication.

10.8.5.2 CAN: CPU Write Access (More Than

One Cycle) Corrupts CAN Frame

Symptoms:

For CAN received messages the identifier high

byte or last data byte can be corrupted.

For CAN transmitted messages the 2nd data byte

can be corrupted.

Details:

The CAN transmit and receive buffers are imple-

mented as dual ported RAM. During the reception

of a CAN frame the CAN core writes the received

identifier and the data byte-by-byte in the corre-

sponding buffer.

IF the CAN bit timing configuration is tBS2 < 5 time

quanta

AND

IF concurrently with the pCAN, the CPU executes

a write access to the dual ported RAM using an in-

struction with more than one cycle access, e.g.

CLR, BSET, BRES

THEN the access conflict can lead to the corrup-

tion described in the symptoms paragraph above.

Impact On The Application:

Several CAN frames with erroneous data or iden-

tifier will be received/transmitted.

Software Workaround:

Program tBS2 > 4 time quanta or, when accessing

the receive or transmit buffers, do not use the crit-

ical instructions which are:

BSET, BRES, CLR, CPL, DEC, INC, NEG, RLC,

SLL, SRL, RRC, SRA, SWAP.

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