16.7.5.2 Precautions for Entering and Exiting Device Low-Power Modes (LPM)
The 28x device features two low-power modes, STANDBY and HALT, in which the peripheral clocks are turned
off. Since the CAN module is connected to multiple nodes across a network, you must take care before entering
and exiting device low-power modes such as STANDBY and HALT. A CAN packet must be received in full
by all the nodes; therefore, if transmission is aborted half-way through the process, the aborted packet would
violate the CAN protocol resulting in all the nodes generating error frames. The node exiting LPM should do so
unobtrusively. For example, if a node exits LPM when there is traffic on the CAN bus it could “see” a truncated
packet and disturb the bus with error frames.
The following points must be considered before entering a device low-power mode:
1. The CAN module has completed the transmission of the last packet requested.
2. The CAN module has signaled to the CPU that it is ready to enter LPM.
In other words, device low-power modes should be entered into only after putting the CAN module in local
power-down mode.
16.7.5.3 Enabling or Disabling Clock to the CAN Module
The CAN module cannot be used unless the clock to the module is enabled. It is enabled or disabled by using
bit 14 of the PCLKCR0 register for eCAN-A module . This bit is useful in applications that do not use the CAN
module at all. In such applications, the CAN module clock can be permanently turned off, resulting in some
power saving. This bit is not intended to put the CAN module in low-power mode and should not be used for that
purpose. Like all other peripherals, clock to the CAN module is disabled upon reset.
16.7.5.4 Possible Failure Modes External to the CAN Controller Module
This section lists some potential failure modes in a CAN based system. The failure modes listed are external to
the CAN controller and hence, need to be evaluated at the system level.
• CAN_H and CAN_ L shorted together
• CAN_H and/or CAN_ L shorted to ground
• CAN_H and/or CAN_ L shorted to supply
• Failed CAN transceiver
• Electrical disturbance on CAN bus
16.8 Acceptance Filter
The identifier of the incoming message is first compared to the message identifier of the mailbox (which is stored
in the mailbox). Then, the appropriate acceptance mask is used to mask out the bits of the identifier that should
not be compared.
In the SCC-compatible mode, the global acceptance mask (GAM) is used for the mailboxes 6 to 15. An incoming
message is stored in the highest numbered mailbox with a matching identifier. If there is no matching identifier in
mailboxes 15 to 6, the incoming message is compared to the identifier stored in mailboxes 5 to 3 and then 2 to 0.
The mailboxes 5 to 3 use the local-acceptance mask LAM(3) of the SCC registers. The mailboxes 2 to 0 use the
local-acceptance mask LAM(0) of the SCC registers. For specific uses, see
To modify the global acceptance mask register (CANGAM) and the two local-acceptance mask registers of the
SCC, the CAN module must be set in the initialization mode (see
).
In eCAN mode, each of the 32 mailboxes has its own local-acceptance mask LAM(0) to LAM(31). There is no
global-acceptance mask in the eCAN mode.
The selection of the mask to be used for the comparison depends on which mode (SCC or eCAN) is used.
Controller Area Network (CAN)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
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Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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