cp3bt13 National Semiconductor Corporation, cp3bt13 Datasheet - Page 106

• Manufacturer Part Number: cp3bt13
• Description: Cp3bt13 Reprogrammable Connectivity Processor With Bluetooth-r And Can Interfaces
• Manufacturer: National Semiconductor Corporation

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DRIVE
16.10.17 CAN Timer Register (CTMR)
The CTMR register reports the current value of the Time
Stamp Counter as described in Section 16.8.
The CTMR register is a free running 16-bit counter. It con-
tains the number of CAN bits recognized by the CAN mod-
ule since the register has been cleared. The counter starts
to increment from the value 0000b after a hardware reset. If
the Timer Stamp Enable bit (TSTPEN) in the CAN global
configuration register (CGCR) is set, the counter will also be
cleared on a message transfer of the message buffer 0.
The contents of CTMR are captured into the Time Stamp
register of the message buffer after successfully sending or
receiving a frame, as described in “Time Stamp Counter” on
page 92.
16.11
After system start-up, all CAN-related registers are in their
reset state. The CAN module can be enabled after all con-
figuration registers are set to their desired value. The follow-
ing initial settings must be made:
T Configure the CAN Timing register (CTIM). See “Bit
T Configure every buffer to its function as receive/transmit.
T Set the acceptance filtering masks. See “Acceptance Fil-
T Enable the CAN interface. See “CAN Global Configura-
Before disabling the CAN module, software must make sure
that no transmission is still pending.
Note: Activity on the CAN bus can wake up the device from
a reduced-power mode by selecting the CANRX pin as an
input to the Multi-Input Wake-Up module. In this case, the
CAN module must not be disabled before entering the re-
duced-power mode. Disabling the CAN module also dis-
ables the CANRX pin. As an alternative, the CANRX pin can
be connected to any other input pin of the Multi-Input Wake-
Up module. This input channel must then be configured to
trigger a wake-up event on a falling edge (if a dominant bit
is represented by a low level). In this case, the CAN module
can be disabled before entering the reduced-power mode.
After waking up, software must enable the CAN module
again. All configuration and buffer registers still contain the
same data they held before the reduced-power mode was
entered.
15
Time Logic” on page 83.
See “Buffer Status/Control Register (CNSTAT)” on
page 94.
tering” on page 85.
tion Register (CGCR)” on page 99.
SYSTEM START-UP AND MULTI-INPUT
WAKE-UP
The Drive bit shows the output value on the
CANTX pin at the time of the error. Note that
a receiver will not drive the bus except during
ACK and during an active error flag.
CTMR15:0
R
0
0
106
16.11.1 External Connection
The CAN module uses the CANTX and CANRX pins to con-
nect to the physical layer of the CAN interface. They provide
the functionality described in Table 54.
The logic levels are configurable by the CTX and CRX bits
of the Global Configuration Register CGCR (see “CAN Glo-
bal Configuration Register (CGCR)” on page 99).
16.11.2 Transceiver Connection
An external transceiver chip must be connected between
the CAN block and the bus. It establishes a bus connection
in differential mode and provides the driver and protection
requirements. Figure 52 shows a possible ISO-High-Speed
configuration
16.11.3 Timing Requirements
Processing messages and updating message buffers re-
quire a certain number of clock cycles, as shown in
Table 55. These requirements may lead to some restrictions
regarding the Bit Time Logic settings and the overall CAN
performance which are described below in more detail. Wait
cycles need to be added to the cycle count for CPU access
to the object memory as described in CPU Access to CAN
Registers/Memory on page 93. The number of occurrences
per frame is dependent on the number of matching identifi-
ers.
Signal Name
CANRX
CR16CAN
CANTX
CPU Bus
CANTX
CANRX
Figure 52. External Transceiver
.
Table 54 External CAN Pins
Output
Type
Input
5
4
1
REF
RX
TX
Transceiver Chip
8
RS
Receive data from the CAN bus
Transmit data to the CAN bus
BUS_H
BUS_L
GND
2
VCC
3
7
6
Description
VCC
120
120
Termination
CAN bus
signals
To other
modules
DS048