Civil Engineering Reference
In-Depth Information
• Jitter on the received edges caused by radio frequency (RF) fields lowers the
precision of the calibration result; increasing the immunity of the transceiver
would increase current consumption and, in any case, could only be achieved to
a limited extent.
• Oversampling is needed to achieve a sufficient level of precision; the higher the
oversampling rate, the higher the current consumption.
• Ringing on the recessive edges means that they cannot be used for calibration.
• Messages that occur after silence on the bus are not defined and thus can be
transmitted in a number of different formats; in the worst case, there are only
four dominant edges in a message (ID = 0E0h, RTR = 1, DLC = 1).
• The ID field can be disturbed by arbitration and, therefore, cannot be used for
calibration; moreover, the non-calibrated receiver does not know where the ID
field ends (note that the ID can be 11 bit or 29 bit).
• Car makers require calibration to be completed by the time five messages have
been received; otherwise, start-up will take too long and wake-up events might
be missed.
• Errors such as “stuff error”, “form error”, “CRC error” or error frames can dis-
turb the calibration process.
• Transmitter clock tolerances (up to ± 0.5 % according to SAE bit-timing require-
ments) lead to errors in the calibration results. This is critical when the receiver
clock has been tuned to a slow sender and the wake-up message is sent by a fast
sender (or vice versa).
NXP transceivers with partial networking have the same state diagram as standard
transceivers like the TJA1041(A) or TJA1043. So the familiar “normal”, “standby”
and “sleep” modes are available in the new transceiver generation. The only differ-
ence is in the wake-up mechanism; the new transceivers will only respond to the
configured WUFs.
To achieve good emission performance throughout the system, pins CAN_H and
CAN_L are biased towards 2.5 V when the transceiver is in a low-power mode
(standby or sleep) and bus traffic is being monitored for wake-up messages. Bias-
ing is turned off automatically if the bus is silent for more than a second. Standard
transceivers always terminate the CAN_H and CAN_L pins to GND when in a
low-power mode, enforcing a common-mode step with every message transmitted
on the bus.
2.6
Transceiver Implementations
2.6.1
Implementation Example TLE 6254 3G (ISO
11898-3)
TLE 6254-3G is a standard low-speed CAN transceiver of Infineon technologies
with an excellent EMC performance and a high ESD robustness. All transceiver
