ST72521 STMICROELECTRONICS [STMicroelectronics], ST72521 Datasheet - Page 146

• 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)
Software Work-around - Devices with Hard-
ware Fix (ST72F521 rev “R”):
To implement a transmission abort under safe
conditions, the LOCK bit must not be reset during
the critical window (2 bit times). A new function
has been implemented in the MCU allowing the
application to synchronize the reset of the LOCK
bit (abort request) with the reset of the TXRQST bit
(internal signal) in the pCAN core.
The synchronization is done using the WKPS bit in
the CANCSR register, the function of this bit has
been modified and no more Wake-up Pulse (dom-
inant bit) is sent on the CAN_TX signal when the
WKPS bit is set. This means the the functionality
described in the datasheet is no longer applicable
(see
146/211
CANCSR |= WKPS;
while(!(CANCSR & WKPS) );// Wait until WKPS bit is set
while( CANBCSR & LOCK )// Wait until abort has been confirmed
{
}
CANCSR &= ~WKPS;
CANBCSR |= LOCK;
Section
10.8.5.4).
CANBCSR &= ~LOCK;
// Set WKPS bit
// Allow transmission again
//Alloc buffer for next transmission
To abort the transmission, first the application sets
the WKPS bit and polls it until it is set. The maxi-
mum time needed to set this bit is two CAN bit
times. Once the application has read the WKPS bit
as one, it can reset the LOCK bit to stop the cur-
rent transmission.
The abort is completed when the LOCK bit is read
back as zero by the application. Once the abort
has been completed, the application must reset
the WKPS bit to be able to transmit again. Of
course the transmit buffer must be in LOCK state
as usual before any transmission attempt.
The “C” code sequence below shows the software
work-around using the WKPS bit.