C515C_9711 Datasheet, PDF (156/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
Bit
RMTPND
TXRQ
MSGLST
CPUUPD
NEWDAT
Function
Remote pending (used for transmit-objects)
Indicates that the transmission of this message object has been requested by a
remote node, but the data has not yet been transmitted. When RMTPND is set,
the CAN controller also sets TXRQ. RMTPND and TXRQ are cleared, when the
message object has been successfully transmitted.
Transmit request
Indicates that the transmission of this message object is requested by the CPU or
via a remote frame and is not yet done. TXRQ can be disabled by CPUUPD. ^{1) 3)}
Message lost (this bit applies to receive-objects only!)
Indicates that the CAN controller has stored a new message into this object, while
NEWDAT was still set, ie. the previously stored message is lost.
CPU update (this bit applies to transmit-objects only!)
Indicates that the corresponding message object may not be transmitted now. The
microcontroller sets this bit in order to inhibit the transmission of a message that
is currently updated, or to control the automatic response to remote requests.
New data
Indicates, if new data has been written into the data portion of this message object
by microcontroller (transmit-objects) or CAN controller (receive-objects) since this
bit was last reset, or not. ²⁾
1) In message object 15 (last message) these bits are hardwired to “0” (inactive) in order to
prevent transmission of message 15.
2) When the CAN controller writes new data into the message object, unused message bytes will
be overwritten by non specified values. Usually the microcontroller will clear this bit before
working on the data, and verify that the bit is still cleared once it has finished working to ensure
that it has worked on a consistent set of data and not part of an old message and part of the
new message.
For transmit-objects the microcontroller will set this bit along with clearing bit CPUUPD. This
will ensure that, if the message is actually being transmitted during the time the message was
being updated by the microcontroller, the CAN controller will not reset bit TXRQ. In this way bit
TXRQ is only reset once the actual data has been transferred.
3) When the microcontroller requests the transmission of a receive-object, a remote frame will be
sent instead of a data frame to request a remote node to send the corresponding data frame.
This bit will be cleared by the CAN controller along with bit RMTPND when the message has
been successfully transmitted, if bit NEWDAT has not been set. If there are several valid
message objects with pending transmission request, the message with the lowest message
number is transmitted first.
Semiconductor Group
6-93
1997-11-01