Tx
Rx
CAN Core
•
•
=1
DCAN
CAN_RX
CAN_TX
Functional Description
Figure 23-8. CAN Core in Loop Back Combined With Silent Mode
23.3.8.3.5 Software Control of CAN_TX pin
Four output functions are available for the CAN transmit pin CAN_TX. In addition to its default function
(serial data output), the CAN_TX pin can drive constant dominant or recessive values, or it can drive the
CAN sample point signal to monitor the CAN core’s bit timing.
Combined with the readable value of the CAN_RX pin, this function can be used to check the physical
layer of the CAN bus.
The output mode of pin CAN_TX is selected by programming the test register bits Tx[1:0] as described in
section .
NOTE:
The software control for the CAN_TX pin interferes with CAN protocol functions. For CAN
message transfer or any of the test modes (loopback mode, external loopback mode or silent
mode), the CAN_TX pin should operate in its default functionality.
23.3.9 Dual Clock Source
Two clock domains are provided to the DCAN module: the peripheral synchronous clock domain
(L3_SLOW_GCLK) as the general module clock source, and the peripheral asynchronous clock source
domain (CLK_M_OSC) provided to the CAN core (as clock source CAN_CLK) for generating the CAN bit
timing.
Both clock domains can be derived from the same clock source (so that L3_SLOW_GCLK =
CLK_M_OSC).
For more information on how to configure the relevant clock source registers in the system module, see
, Power and Clock Management.
Between the two clock domains, a synchronization mechanism is implemented in the DCAN module in
order to ensure correct data transfer.
NOTE:
If the dual clock functionality is used, then L3_SLOW_GCLK must always be higher or equal
to CAN_CLK (CLK_M_OSC) (derived from the asynchronous clock source), in order to
achieve a stable functionality of the DCAN. Here also the frequency shift of the modulated
L3_SLOW_GCLK has to be considered:
f
0
,
L3_SLOW_GCLK
(OCP) ±
Δ
f
FM
,
L3_SLOW_GCLK
(OCP)
≥
f
CANCLK
3893
SPRUH73H – October 2011 – Revised April 2013
Controller Area Network (CAN)
Copyright © 2011–2013, Texas Instruments Incorporated