CP3BT23_14 Datasheet, PDF (167/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
www.ti.com
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
Example 2
PSC = PSC[5:0] + 1 = 2 + 2 = 4
TSEG1 = TSEG1[3:0] + 1 = 1 + 1 = 2
TSEG2 = TSEG2[2:0] + 1 = 0 + 1 = 1
SJW = TSEG2 = 1
• Sample point positioned at 75% of bit time
• Bit time = 250 ns × (1 + 2 + 1 M 1) = (1 M 0.25) µs
• Bus Clock = 16 MHz / (2 × (1 + 4 + 3)) = 1Mbit/s (nominal)
18.11.5 Acceptance Filter Considerations
The CAN module provides two acceptance filter masks GMSK and BMSK, as described in Section 18.4,
Section 18.10.8, and Section 18.10.9. These masks allow filtering of up to 32 bits of the message object,
which includes the standard identifier, the extended identifier, and the frame control bits RTR, SRR, and
IDE.
18.11.6 Remote Frames
Remote frames can be automatically processed by the CAN module. However, to fully enable this feature,
the RTR/ XRTR bits (for both standard and extended frames) within the BMSK and/or GMSK register
need to be set to “don’t care”. This is because a remote frame with the RTR bit set should trigger the
transmission of a data frame with the RTR bit clear and therefore the ID bits of the received message
need to pass through the acceptance filter. The same applies to transmitting remote frames and switching
to receive the corresponding data frames.
18.12 USAGE HINT
Under certain conditions, the CAN module receives a frame sent by itself, even though the loopback
feature is disabled. Two conditions must be true to cause this malfunction:
• A transmit buffer and at least one receive buffer are configured with the same identifier. Assume this
identifier is called ID_RX_TX. With regard to the receive buffer, this means that the buffer identifier and
the corresponding filter masks are set up in a way that the buffer is able to receive frames with the
identifier ID_RX_TX.
• The following sequence of events occurs:
1. A message with the identifier ID_RX_TX from another CAN node is received into the receive buffer.
2. A message with the identifier ID_RX_TX is sent by the CAN module immediately after the reception
took place.
When these conditions occur, the frame sent by the CAN module will be copied into the next receive
buffer available for the identifier ID_RX_TX.
If a frame with an identifier different to ID_RX_TX is sent or received in between events 1 and 2, the
problem does not occur.
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CAN Module 167