cp3cn17 National Semiconductor Corporation, cp3cn17 Datasheet - Page 83

• Manufacturer Part Number: cp3cn17
• Description: Reprogrammable Connectivity Processor With Can Interface
• Manufacturer: National Semiconductor Corporation

ity is combined by the 4-bit TXPRI value and the 4-bit buffer
number (0...14) as shown below. The lowest resulting num-
ber results in the highest transmit priority.
Table 34 shows the transmit priority configuration if the pri-
ority is TXPRI = 0 for all transmit buffers:
Table 35 shows the transmit priority configuration if TXPRI
is different from the buffer number:
Note: If two buffers have the same priority (PRI), the buffer
with the lower buffer number will have the higher priority.
7
TXPRI
TXPRI
14
13
12
11
10
0
0
0
9
8
7
6
5
4
3
2
1
0
:
:
Table 35 Transmit Priority (TXPRI not 0)
Table 34 Transmit Priority (TXPRI = 0)
TXPRI
Number
Number
Buffer
Buffer
14
10
11
12
13
14
0
1
0
1
2
3
4
5
6
7
8
9
:
:
4
3
PRI
PRI
224
209
194
179
164
149
134
119
104
14
89
74
59
44
29
14
0
1
:
:
BUFFER #
TX Priority
TX Priority
Highest
Highest
Lowest
Lowest
:
:
0
83
15.6.3
The transmission of a CAN message must be executed as
follows (see also Figure 35)
Writing TX_ONCE or TX_ONCE_RTR in the CNSTAT sta-
tus 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.
1. Configure
2. Load buffer identifier and data registers. (For remote
3. Configure the CNSTAT status field to the desired value:
— TX_ONCE to trigger the transmission process of a
— TX_ONCE_RTR to trigger the transmission of a sin-
— TX_RTR waits for a remote frame to trigger the trans-
TX_NOT_ACTIVE. If the status is TX_BUSY, a previ-
ous 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 be-
comes 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 trans-
mission is aborted by an error.
frames the RTR bit of the identifier needs to be set and
loading data bytes can be omitted.)
single frame.
gle data frame and then wait for a received remote
frame to trigger consecutive data frames.
mission of a data frame.
Transmit Procedure
Figure 35. Buffer Write Routine
the
TX_NOT_ACTIVE
TX_ONCE_RTR
Write ID/data
TX_BUSYx?
Write_buffer
TX_ONCE
TX_RTR
CNSTAT
Write
Write
Exit
or
or
No
DS041
status
Yes
www.national.com
field
as