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Module Operation
1247
SPNU563A–March 2018
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FlexRay Module
NOTE: In case of an odd payload length (PLC=1,3,5,...) the application needs to write zeros to the
last 16 bit of the message buffers data section to ensure that the padding pattern is all zeros.
Each transmit buffer provides a transmission mode flag TXM that allows the host to configure the
transmission mode for the transmit buffer. If this bit is set, the transmitter operates in the single-shot
mode. If this bit is cleared, the transmitter operates in the continuous mode.
In single-shot mode the Communication Controller resets the corresponding TXR flag after transmission
has completed after which the host may update the transmit buffer.
In continuous mode, the Communication Controller does not reset the corresponding transmission request
flag TXR after successful transmission. In this case a frame is sent out each time the filter criteria match.
The TXR flag can be reset by the Host by writing the corresponding message buffer number to the IBCR
register while bit IBCM.STXRH is set to 0.
If two or more transmit buffers meet the filter criteria simultaneously, the transmit buffer with the lowest
message buffer number will be transmitted in the corresponding slot.
26.2.9.4 Frame Transmission
The following steps are required to prepare a message buffer for transmission:
• Configure the transmit buffer in the Message RAM through WRHS1, WRHS2, and WRHS3
• Write the data section of the transmit buffer through WRDSn
• Transfer the configuration and message data from Input Buffer to the Message RAM by writing the
number of the target message buffer to register IBCR
• If configured in the Input Buffer Command Mask (IBCM) register the Transmission request flag (TXR)
for the corresponding message buffer will be set as soon as the transfer has completed, and the
message buffer is ready for transmission.
• Check whether the message buffer has been transmitted by checking the TXR bits (TXR = 0) in the
Transmission request 1,2,3,4 registers (single-shot mode only).
After transmission has completed, the corresponding TXR flag in the Transmission request 1,2,3,4 register
is reset (single- shot mode), and, if bit MBI in the header section of the message buffer is set, flag SIR.TXI
in the Status Interrupt register is set to 1. If enabled, an interrupt is generated.
26.2.9.5 Null Frame Transmission
If in static segment the host does not set the transmission request flag before transmit time, and if there is
no other transmit buffer with matching filter criteria, the communication controller transmits a null frame
with the null frame indication bit set and the payload data cleared to 0.
In the following cases the communication controller transmits a null frame:
• If the message buffer with the lowest message buffer number matching the filter criteria does not have
its transmission request flag set (TXR = 0).
• No transmit buffer configured for the slot has a cycle counter filter that matches the current cycle. In
this case, no message buffer status MBS is updated.
Null frames are not transmitted in the dynamic segment.
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