Table 16-16. Remote-Frame-Pending Register (CANRFP) Field Descriptions
Bit
Field
Value
Description
31:0
RFP.31:0
Remote-frame-pending register.
For a receive mailbox, RFP
n
is not set if a remote frame is received and TRS
n
is not affected.
For a transmit mailbox, RFP
n
is set if a remote frame is received and TRS
n
is set if AAM of the
mailbox is 1. The ID of the mailbox must match the remote frame ID.
1
A remote-frame request was received by the module.
0
No remote-frame request was received. The register is cleared by the CPU.
16.9.9.1 Handling of Remote Frames
If a remote frame is received (the incoming message has the RTR bit set), the CAN module compares the
identifier to all identifiers of the mailboxes using the appropriate masks starting at the highest mailbox number in
descending order.
In the case of a matching identifier (with the message object configured as send mailbox and AAM (MSGID.29)
in this message object set) this message object is marked as to be sent (TRS[
n
] is set).
In case of a matching identifier with the mailbox configured as a send mailbox and bit AAM in this mailbox is not
set, this message is not received in that mailbox.
After finding a matching identifier in a mailbox no further compare is done.
With a matching identifier and the message object configured as receive mailbox, this message is handled like a
data frame and the corresponding bit in the receive message pending (CANRMP) register is set. The CPU then
has to decide how to handle this situation. For information about the CANRMP register, see
.
For the CPU to change the data in a mailbox that is configured as a remote frame mailbox (AAM set) it has to set
the mailbox number and the change data request (CDR) bit [CANMC.8] first. The CPU can then write the new
data and clear the CDR bit to indicate to the eCAN that the access is finished. Until the CDR bit is cleared, the
transmission of this mailbox is not permitted. Therefore, the newest data is sent.
To change the identifier in that mailbox, the mailbox must be disabled first (CANME
n
= 0).
For the CPU to request data from another node it configures the mailbox as a receive mailbox and sets the TRS
bit. In this case the module sends a remote frame request and receives the data frame in the same mailbox that
sent the request. Therefore, only one mailbox is necessary to do a remote request. Note that the CPU must set
RTR (MSGCTRL.4) to enable a remote frame transmission. Once the remote frame is sent, the TRS bit of the
mailbox is cleared by CAN. In this case, bit TA
n
will not be set for that mailbox.
The behavior of the message object
n
is configured with CANMD[
n
] (CANMD.31-0), the AAM (MSGID.29), and
RTR (MSGCTRL.4). It shows how to configure a message object according to the desired behavior.
To summarize, a message object can be configured with four different behaviors:
1. A transmit message object is only able to transmit messages.
2. A receive message object is only able to receive messages.
3. A remote-request message object is able to transmit a remote request frame and to wait for the
corresponding data frame.
4. A auto-reply message object is able to transmit a data frame whenever a remote request frame is received
for the corresponding identifier.
Note
When a remote transmission request is successfully transmitted with a message object configured in
request mode, the CANTA register is not set and no interrupt is generated. When the remote reply
message is received, the behavior of the message object is the same as a message object configured
in receive mode.
Controller Area Network (CAN)
1030
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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