CP3SP33SMSSLASHNOPB datasheet(191/407 Pages) TI1

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Exit

Write_buffer

Write

TX_ONCE

TX_ONCE_RTR

TX_RTR

Write

TX_NOT_ACTIVE

Write ID/data

TX_BUSYx?

Yes

DS041

CP3SP33

www.ti.com

SNOSCW5 – MAY 2013

Table 22-4. Transmit Priority (TXPRI not 0) (continued)

TXPRI

BUFFER NUMBER

PRI(1)

TX PRIORITY

Highest

22.6.3 Transmit Procedure

The transmission of a CAN message must be executed as follows (see Figure 22-24)

1. Configure the CNSTAT status field as TX_NOT_ACTIVE. If the status is TX_BUSY, a previous

transmit request is still pending and software has no access to the data contents of the buffer. In that

case, software may choose to wait until the buffer becomes available again as shown. Other options

are to exit from the update routine until the buffer has been transmitted with an interrupt generated, or

the transmission is aborted by an error.

2. Load buffer identifier and data registers. (For remote frames the RTR bit of the identifier needs to be

set and loading data bytes can be omitted.)

3. Configure the CNSTAT status field to the desired value:

–

TX_ONCE to trigger the transmission process of a single frame.

–

TX_ONCE_RTR to trigger the transmission of a single data frame and then wait for a received

remote frame to trigger consecutive data frames.

–

TX_RTR waits for a remote frame to trigger the transmission of a data frame.

Writing TX_ONCE or TX_ONCE_RTR in the CNSTAT status field will set the internal transmit request for

the CAN module.

If a buffer is configured as TX_RTR and a remote frame is received, the data contents of the addressed

buffer will be transmitted automatically without further CPU activity.

Figure 22-24. Buffer Write Routine

Dual CAN Interfaces

191

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