8.2 CAN interface circuitry
Controller Area Network (CAN) is commonly used in almost all automotive applications to allow communication between
various microchips in the car.
The number of CAN modules on-chip vary from device to device. A separate CAN transceiver is required for each CAN
module, although some CAN transceivers may have more than one on a single chip.
Freescale CAN modules conform to CAN protocol specification version 2.0B, and the transceivers shown in this Hardware
design guide comply with ISO11898 physical layer standard.
Typically, CAN is used at either a low speed (5 Kbps to 125 Kbps) or a high speed (250 Kbps to 1 Mbps). Power train
applications typically use a high speed (HS) CAN interface to communicate between the engine control unit and the
transmission control unit. Body and chassis applications typically use a low speed (LS) CAN interface. In the dashboard of a
vehicle, there is typically a gateway device that interfaces between HS and LS CAN networks.
Popular CAN transceivers include the NXP devices in the table below. Example TJA1050 HS and TJA1054 LS circuits are
shown in this Hardware design guide .
Table 15. NXP CAN transceiver comparison
TJA1050
TJA1054
TJA1040
TJA1041
Bit-rate (Kbps)
1000
125
1000
1000
Modes of operation
Normal, listen only
Normal, standby, sleep Normal, standby
Normal, listen only,
standby, sleep
8.2.1 High-speed CAN TJA1050 interface
Figure 9
shows the typical connections for the physical interface between the MCU and the CAN bus for HS applications
using the NXP TJA1050 HS CAN transceiver.
MCU_CAN_TXD
VREF
MCU_CAN_RXD
CANH
CANL
+5V
60 Ω
60 Ω
60 Ω
60 Ω
10K
4700 pF
U1
TJA1050T
U1
TJA1050T
GND
2
VCC
3
CANH
7
CANL
6
S
8
TXD
1
RXD
4
VREF
5
4700 pF
4700 pF
++
10 uF
Figure 9. Typical high-speed CAN circuit using TJA1050
Example communication peripheral connections
Hardware Design Guide, Rev. 0, 2012
Freescale Semiconductor, Inc.
17
