CP3BT23 Datasheet, PDF (106/260 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

that case the procedure described below must be fol-
Read buffer
lowed.
2. Read the status to determine if a new message has
overwritten the one originally received which triggered
the interrupt.
Read CNSTAT
3. Write RX_READY into CNSTAT.
4. Read the ID/data and object control (DLC/RTR) from
the message buffer.
Yes
RX_READY?
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.
No
6. If the buffer status is RX_FULL or RX_OVERRUN, one
Yes
RX_BUSYx?
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
Figure 52.
No
Interrupt Entry Point
RX_OVERRUN?
(optional, for information)
te ^{Write RX_READY}
Read buffer (id/data/control)
2), clear interrupt pending bit and exit.
When the BUFFLOCK function is enabled (see BUFFLOCK
on page 102), it is not necessary to check for new messag-
es 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 53.
Interrupt Entry Point
Read buffer (id/data/control)
le ^{Read CNSTAT}
Write RX_READY
Yes
RX_BUSYx?
Clear RX_PND
o _No
Exit
RX_FULL or
Yes
RX_OVERRUN?
DS039
s _No
Figure 53. Buffer Read Routine (BUFFLOCK Enabled)
Clear RX_PND
For simplicity only the applicable interrupt routine is shown:
b ^{1. Read the ID/data and object control (DLC/RTR) from}
the message buffer.
Exit
DS038
2. Write RX_READY into CNSTAT.
3. Clear interrupt pending bit and exit.
O^{Buffer Read Routine (BUFFLOCK Disabled) 18.5.3 RX Buffer States}
The first step is only applicable if polling is used to get the As shown in Figure 53, a receive procedure starts as soon
status of the receive buffer. It can be deleted for an interrupt as software has set the buffer from the RX_NOT_ACTIVE
driven receive routine.
state into the RX_READY state. The status section of CN-
1. Read the status (CNSTAT) of the receive buffer. If the
status is RX_READY, no was the message received, so
exit. If the status is RX_BUSY, the copy process from
hidden receive buffer is not completed yet, so read CN-
STAT again.
STAT 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
If a buffer is configured to RX_READY and its interrupt
is enabled, it will generate an interrupt as soon as the
buffer has received a message and entered the
RX_FULL state (see also Interrupts on page 108). In
the buffer. In the second case, the buffer state will automat-
ically 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
105
www.national.com