XC161 Datasheet, PDF (278/419 Pages) Infineon Technologies AG – 16-Bit Single-Chip Microcontroller with C166SV2 Core Volume 2 (of 2): Peripheral Units

XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
TwinCAN Module
When a shared gateway message object, set up as receive object on the source side
(lower left state bubble in Figure 21-22), receives a data frame while GDFS is set to ‘1’,
it commutes to a transmission object on the destination side by toggling control bits
NODE and DIR and sends the corresponding data frame without any CPU interaction
(upper left state bubble).
Depending on control bit SRREN, the shared gateway message object returns to its
initial function as receive object assigned to the source side (SRREN = ‘0’: state
transition 2 to the lower left state bubble in Figure 21-22) or remains assigned to the
destination side waiting for a remote frame with matching identifier (SRREN = ‘1’: state
transition 3 to the upper right state bubble).
When the shared gateway message object is assigned as transmit object to the
destination side (upper right state bubble), it responds to remote frames received on the
destination side. If bit SRREN is cleared, the remote request is directly answered by a
data frame based on the contents of the gateway message object (state transition 4 to
the upper left state bubble).
If bit SRREN is set and a remote frame is received on the destination side, the shared
gateway message object commutes to a receive object on the source side by toggling
control bits NODE and DIR and prepares the emission of the received remote frame by
setting TXRQ and RMTPND to ‘10’ (state transition 5 to the lower right state bubble).
Then the shared gateway message object emits the corresponding remote frame without
any CPU interaction (state transition 6 to the lower left state bubble).
The gateway message object remains assigned to the source side until a data frame with
matching identifier arrives (lower left state bubble). Then the shared gateway message
object returns to the destination side and, depending on control bit GDFS, transmits
immediately the corresponding data frame (GDFS = ‘1’, upper left state bubble) or waits
upon an action of the CPU setting TXRQ to ‘10’ (GDFS = ‘0’: state transition 7 to the
upper right state bubble). Alternatively, a remote frame with matching identifier, arriving
on the destination side, may set TXRQ to ‘10’ and initiate the data frame transmission.
If a data frame arrives on the source side while the shared gateway object with matching
identifier is switched to the destination side, the data frame on the source side gets lost.
Due to the temporary assignment to the destination node, the shared gateway message
object does not notice the data frame on the source node and is not able to report the
data loss via control bitfield MSGLST = ‘10’. The probability for a data loss is enlarged,
if the automatic data frame transmission on the destination side is disabled by
GDFS = ‘0’. A corresponding behavior has to be taken into account for incoming remote
frames on the destination bus.
Note: As long as bitfield MSGLST is activated, an incoming data frame cannot be
automatically transmitted on the destination side. Due to the internal toggling of
control bit DIR, the shared gateway object converts from receive to transmit
operation and bitfield MSGLST is interpreted as CPUUPD = ‘10’ preventing the
automatic transmission of a data frame.
User’s Manual
TwinCAN_X1, V2.1
21-38
V2.2, 2004-01