CP3BT23_14 Datasheet, PDF (135/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
www.ti.com
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
18.2.7 Clock Generator
The CAN prescaler (PSC) is shown is Figure 18-14. It divides the CKI input clock by the value defined in
the CTIM register. The resulting clock is called time quanta clock and defines the length of one time
quantum (tq).
Please refer to CAN Timing Register (CTIM) for a detailed description of the CTIM register.
Note: PSC is the value of the clock prescaler. TSEG1 and TSEG2 are the length of time segment 1 and 2
in time quanta.
The resulting bus clock can be calculated by the equation:
busclock = CKI / (PSC) x (1 + TSEG1 + TSEG2)
(16)
The values of PSC, TSEG1, and TSEG2 are specified by the contents of the registers PSC, TSEG1, and
TSEG2 as follows:
PSC = PSC[5:0] + 2
TSEG1 = TSEG1[3:0] + 1
TSEG2 = TSEG2[2:0] + 1
Figure 18-14. CAN Prescaler
18.3 MESSAGE TRANSFER
The CAN module has access to 15 independent message buffers, which are memory mapped in RAM.
Each message buffer consists of 8 different 16-bit RAM locations and can be individually configured as a
receive message buffer or as a transmit message buffer.
A dedicated acceptance filtering procedure enables software to configure each buffer to receive only a
single message ID or a group of messages. One buffer uses independent filtering procedure, which
provides the possibility to establish a BASIC-CAN path.
For reception of data frame or remote frames, the CAN module follows a “receive on first match” rule
which means that a given message is only received by one buffer: the first one which matches the
received message ID.
The transmission of a frame can be initiated by software writing to the transmit status and priority register.
An alternate way to schedule a transmission is the automatic answer to remote frames. In the latter case,
the CAN module will schedule every buffer for transmission to respond to remote frames with a given
identifier if the acceptance mask matches. This implies that a single remote frame is able to poll multiple
matching buffers configured to respond to the triggering remote transmission request.
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