CP3BT23_14 Datasheet, PDF (145/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
www.ti.com
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
18.6.4 TX Buffer States
The transmission process can be started after software has loaded the buffer registers (data, ID, DLC,
PRI) and set the buffer status from TX_NOT_ACTIVE to TX_ONCE, TX_RTR, or TX_ONCE_RTR.
When the CPU writes TX_ONCE, the buffer will be TX_BUSY as soon as the CAN module has scheduled
this buffer for the next transmission. After the frame could be successfully transmitted, the buffer status
will be automatically reset to TX_NOT_ACTIVE when a data frame was transmitted or to RX_READY
when a remote frame was transmitted. If the CPU configures the message buffer to TX_ONCE_RTR, it
will transmit its data contents. During the transmission, the buffer state is 1111b as the CPU wrote 1110b
into the status section of the CNSTAT register. After the successful transmission, the buffer enters the
TX_RTR state and waits for a remote frame. When it receives a remote frame, it will go back into the
TX_ONCE_RTR state, transmit its data bytes, and return to TX_RTR. If the CPU writes 1010b into the
buffer status section, it will only enter the TX_RTR state, but it will not send its data bytes before it waits
for a remote frame. Figure 18-25 illustrates the possible transmit buffer states.
TX_ONCE_RTR
1110
RTR
received
CAN
schedules TX
TX_BUSY2
1111
transmit failed
TX done
TX_RTR
1010
TX request
CPU writes 1110
Transmit
request cancelled
CPU writes 1000
CPU writes 1010
TX request
CPU writes 1100
TX_NOT_ACTIVE
1000
RX_READY
0010
TX_ONCE
1100
TX request delayed
by a TX request of higher
priority message
CAN
schedules TX
TX done
Transmit
request cancelled
CPU writes 1000
Remote transmission
request sent - now wait
to receive a data frame
TX_BUSY0
1101
transmit failed
DS042
Figure 18-25. Transmit Buffer States
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