CP3SP33SMSSLASHNOPB datasheet(188/407 Pages) TI1

188 / 407 page

Exit

Interrupt Entry Point

Clear RX_PND

Write RX_READY

Read buffer (id/data/control)

DS039

CP3SP33

SNOSCW5 – MAY 2013

www.ti.com

5. Read the buffer status again and check it is not RX_BUSYx. If it is, repeat this step until RX_BUSYx

has gone away.

6. If the buffer status is RX_FULL or RX_OVERRUN, one or more messages were copied. In that case,

start over with step 2.

7. If status is still RX_READY (as set by the CPU at step 2), clear interrupt pending bit and exit.

When the BUFFLOCK function is enabled (see BUFFLOCK in section Section 22.4), it is not necessary to

check for new messages received during the read process from the buffer, as this buffer is locked after

the reception of the first valid frame. A read from a locked receive buffer can be performed as shown in

Figure 22-22.

Figure 22-22. Buffer Read Routine (BUFFLOCK Enabled)

For simplicity only the applicable interrupt routine is shown:

1. Read the ID/data and object control (DLC/RTR) from the message buffer.

2. Write RX_READY into CNSTAT.

3. Clear interrupt pending bit and exit.

22.5.3 Rx Buffer States

As shown in Figure 22-22, a receive procedure starts as soon as software has set the buffer from the

RX_NOT_ACTIVE state into the RX_READY state. The status section of CNSTAT register is set from

0000b to 0010b. When a message is received, the buffer will be RX_BUSYx during the copy process from

the hidden receive buffer into the message buffer. Afterwards this buffer is RX_FULL. The CPU can then

read the buffer data and either reset the buffer status to RX_READY or receive a new frame before the

CPU reads the buffer. In the second case, the buffer state will automatically change to RX_OVERRUN to

indicate that at least one message was lost. During the copy process the buffer will again be RX_BUSYx

for a short time, but in this case the CNSTAT status section will be 0101b, as the buffer was RX_FULL

(0100b) before. After finally reading the last received message, the CPU can reset the buffer to

RX_READY.

188

Dual CAN Interfaces

Submit Documentation Feedback

Product Folder Links :CP3SP33

CP3SP33SMS/NOPB Datasheet(PDF) 188 Page - Texas Instruments