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CY8CKIT-017 CAN/LIN Expansion Board Kit Guide, Doc. # 001-57814 Rev. *D
Hardware
4.2
CAN Physical Layer Transceiver Circuit
The CAN physical layer transceiver circuit on the expansion board uses a TJA1050 CAN transceiver
device. This device translates differential CAN bus signals to and from digital CMOS signals with
standard TTL voltage levels.
Three signals are used between this circuit and the PSoC controller. These signals are CAN_RX,
CAN_TX, and CAN_EN. Any data signals on the CAN bus are driven at the CAN_RX signal. Any
data signals driven on the CAN_TX signal is driven onto the CAN bus. The CAN_EN signal enables
and disables the CAN transceiver.
A pull-up resistor footprint (R1) is provided on the CAN_EN net. This can be populated if it is desired
to have a pull-up resistor on the CAN_EN net.
See the TJA1050 device datasheet for details on each of these three pins of the CAN transceiver.
4.2.1
CAN Bus Clock Accuracy
For accurate CAN communication, a CAN controller device must typically have a clock source with a
frequency tolerance of 0.5% or less. Therefore, the PSoC device used as the CAN controller must
meet this requirement. If the native internal oscillator tolerance of the PSoC device is greater than
0.5%, then some external clock source that is more accurate must be used. For example, an
external oscillator or an external crystal can be used with the PSoC to improve the accuracy of the
clocks in the PSoC device.
Footprints for oscillator and crystal devices (and any necessary passive components) are provided
on the CY8CKIT-001 DVK board and PSoC processor module boards. Newer versions of these
boards already have these footprints populated with components. If you have an older PSoC
processor module that does not have a populated crystal circuit, you can populate it yourself or
contact Cypress Technical Support for assistance.
See
Design Wide Resources on page 48
for details on the clock configuration of this kit's code
examples.
4.2.2
CAN Bus Connector
The following table shows the pinout of the CAN DB9 connector (P2) on the expansion board.
Table 4-1. CAN Connector Pinout
By default, pin 9 of the CAN connector is left floating. However, if the CANEXTPWR jumper (JP3) is
populated, pin 9 of the CAN connector is connected to the VIN power rail of the DVK and EBK. This
Pin
Signal
1
NC
2
CAN_L
3
GND
4
NC
5
NC
6
GND
7
CAN_H
8
NC
9
NC (VIN)
