ST72521 STMICROELECTRONICS [STMicroelectronics], ST72521 Datasheet - Page 150

• Manufacturer Part Number: ST72521
• Description: 8-BIT MCU WITH NESTED INTERRUPTS, FLASH, 10-BIT ADC, FIVE TIMERS, SPI, SCI, I2C, CAN INTERFACE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST72521
CONTROLLER AREA NETWORK (Cont’d)
The worst case is when the abort request is done
when the transmission has just started. In this
case the LOCK bit cannot be reset as long as the
BUSY bit is set, this means until the end of the
frame. So the application will wait for READY to be
reset during the whole frame and in this case the
worst case will be the longest frame the applica-
tion is expected to transmit.
Figure 80. Abort with the software work-around
- by NRTX, BUSY and LOCK
Using the software work-around the worst case
occurs in the arbitration lost case. If the abort is re-
quested just after pCAN has lost the arbitration
then the application has to wait for the next falling
edge of the BUSY bit before the LOCK bit can be
reset. If the next arbitration is won by pCAN then
the BUSY bit will be reset by the end of the suc-
cessful transmission. The longest time the applica-
tion has to wait in this case is the time of the long-
est message expected on the bus (minus identifi-
er) plus the longest message expected to be trans-
mitted by the application. This roughly double the
time the application may have to wait before the
abort sequence is performed.
10.8.5.4 WKPS Functionality
Due to a fix implemented to solve the “Unexpected
Message
10.8.5.3) the WKPS functionality has been modi-
fied as follows in Flash ST72F521 devices:
150/211
TX RQST
ABORT RQST
CAN TX
CAN RX
LOCK
READY
BUSY
NRTX
Transmission”
issue
(see
Section
10.8.5.5 Bus-off state not entered
Symptom:
pCAN does not enter bus-off state under certain
conditions. This is fixed in flash ST72F521 Rev R .
Details:
According to the CAN standard, pCAN is expected
to enter bus-off state when TEC (Transmit Error
Counter) is greater than 255.
But if REC (Receive Error Counter) is greater than
127 (Error Passive State) pCAN does not enter
bus-off and the BOFF bit of the CSR register is not
set. To enter bus-off, REC must decrease to a val-
ue lower than 128, this is the case with any correct
reception even if the message is filtered out.
As bus-off state is not entered and pCAN still at-
tempts to transmit its message, after the overflow
the TEC register continues to increment as long as
transmission errors occur.
Impact on the application:
The application will not stop attempting to transmit
CAN messages, even when the bus-off conditions
have been reached, until the transmission has
been successful or the value of REC becomes
lower than 128. However the application will not
disturb the communication of the other nodes on
the CAN network as pCAN is in Error Passive
State.
Flash
ST72F521
Rev R
ROM
ST72521 All
revisions
Device
WKPS bit does not generate a wakeup
pulse. It is used to synchronize the re-
set of the LOCK bit (see
WKPS bit functions according to the
datasheet description.
Work-around - Devices with Hardware
Fix (ST72F521 rev “R”):” on page
Modification
“Software
146)