CANoe DENoe - KEMT FEI TUKE

82
slider is intended to represent the time point of a synchronization edge on the bus,
i.e. the beginning of a bit with recessive-dominant edge. The upper area of the figure
shows the nominal bit timing, i.e. a bit on the bus is depicted as it is expected by the
controller. The lower area of the figure shows the internal controller timing, i.e. the bit
time interval from the controller's perspective. The length of this bit interval depends
on the time point of the arriving synchronization edge:
If the edge falls within the Sync region of nominal timing, then the chip is running
synchronously. If the edge falls within the Tseg1 region of nominal timing, then resynchronization
must be performed. In this case the Tseg1 region is lengthened by up to
SJW (Synchronization Jump Width) BTL cycles. If the edge falls within the Tseg2 region
of nominal timing, then resynchronization must be performed. In this case the
Tseg2 region is shortened by up to SJW (Synchronization Jump Width) BTL cycles. If
no edge falls within nominal timing, this bit time is not utilized for resynchronization.
Disconnecting the Transmit Branch
Since the CAN controller on the PC card represents the interface between the analysis
software and the CAN bus, the bus is influenced by the measurement process. In
particular, the CAN controller gives its acknowledge for correctly recognized messages
by placing a dominant level on the bus at the relevant slot in the CAN message.
To reduce the influence on the system, this functionality can be explicitly deactivated
on the SJA 1000 controller. However, please note that when the acknowledge
is deactivated communication can only occur over the bus if at least one other bus
node sends an acknowledge.
Note: The acknowledge on the CAN-AC2 card can be deactivated as follows:
with 82C200 controller, set the output control register on 0x02 (default is
FA)
with 82527 controller, interrupt the TX line (jumper 9 must be removed on
PB1 resp. PB2)
2.11.3 Acceptance Filtering
With all Basic-CAN controllers on the PC card (SJA 1000/82C200/82527/72005) a
mask controls which messages can be transmitted and which can be received.
For example, the SJA 1000 has one acceptance filter for standard identifiers and one
for extended identifiers, and it expects separate acceptance mask and acceptance
code. The acceptance mask indicates which bit of the ID should be compared with
the acceptance code. If the bit is 1 in the mask, then that particular bit is irrelevant for
the comparison. If it is 0, that bit of the ID is compared with the corresponding bit of
the acceptance code. If these two bits are identical, the message is received; otherwise
it is filtered out. Both the mask and code are entered as hexadecimal numbers.
© Vector Informatik GmbH CANoe/DENoe Manual Version 4.1.1