316
μPD780948, μPD78F0948, μPD780949, μPD78F0949
TXRQn
Transmission Request Flag
0
Write: no transmission requested for this buffer
Read: transmit buffer is free
1
Write: request transmission for buffer n
Read: transmit buffer is occupied by former transmit request
An abort operation can cause different results dependent on the time it is set..
a) Abort is received before the start of the arbitration for transmit.
The TXCn bit is reset showing that the buffer was not send to other nodes.
b) Abort is received during the arbitration, but arbitration is lost.
The TXCn bit is reset showing that the buffer was not send to other nodes.
c) Abort is received during frame transmission, but transmission ends with an error.
The TXCn bit is reset showing that the buffer was not send to other nodes.
d) Abort is received during the frame transmission and transmission ends without error.
The TXCn bit is set showing a successful transfer of the data before the abort gets active.
In all cases the TXRQn bit and the TXAn bit will be cleared at the end of the abort operation, when the
receive buffer is available again.
Cautions:
1. The bits are cleared when the INIT-bit in CANC is set.
2. Writing a 0 to TXAn bit has no influence
The TXCn bit are updated at the End of every frame transmission or abort.
The TXRQn bits have dual function:
1. Request the transmission of a transmit buffer.
2. Inform the CPU whether a buffer is available or is still occupied by a former transmit request.
Setting the transmission request bit requests the CAN to sent the buffer contents onto the bus. The CAN
clears the bit after completion of the transmit. Completion is either a normal transfer free of error or an
abort request.
An error during the transmission does not influence the transmit request status. The DCAN will
automatically retry the transfer.
Cautions:
1. The bits are cleared when the INIT-bit in CANC is set.
2. Writing a 0 to TXR0n bit has no influence
3. Do not use bit operations on this register.
4. Do not change data in transmit buffer n when TXRQn is set.