DS80C390_00 Datasheet, PDF (49/155 Pages) Dallas Semiconductor – High-Speed Microcontroller User’s Guide Supplement

DTUP
Bit 0
DS80C390 High-Speed Microcontroller User’s Guide Supplement
TIH bit to a 0, which will allow the CAN module to send the data requested
by the previous Remote Frame Request. Note that the TIH bit associated with
Message Center 15 is ignored because it is a receive only message center.
CAN 0 Message Center 1 Data Updated. This bit indicates that new data
has been loaded into the data portion of the message center. The exact
function of the DTUP bit is dependent on whether the message center is
configured in a receive (T/ R = 0) or transmit (T/ R = 1) mode. Some
functions are also dependent on the state of the WTOE bit. The DTUP bit is
only cleared by a software write to the bit, a system reset, or the setting of the
CRST bit.
T/ R =0 (receive)
In this mode (T/ R = 0) the DTUP bit is set when new data has been
successfully received and is ready to be read by the microcontroller. The
exact meaning of the DTUP bit during a message center read is determined
by the WTOE bit in the CAN 0 Control Register.
If WTOE = 1 (message center overwrite enabled), DTUP should be
polled before and after reading the message center to ascertain if an
overwrite of the data occurred during the read. For example, software
should clear DTUP before reading the message center and then again
after the message center read. If DTUP has been set, then a new
message was received and software should read the message center
again to read the new data. If DTUP remained cleared, no additional
data was received and the data is complete.
If WTOE=0 the processor is not permitted to overwrite this message
center, so it is only necessary to clear the DTUP bit after reading the
message center.
The state of the DTUP bit in the receive mode does not inhibit remote frame
request transmission in the receive mode. The only gating item for remote
frame transmission in the receive mode is that the MSRDY and MTRQ bits
must both be set.
T/ R =1 (transmit)
In this mode, software must set TIH =1 and clear DTUP = 0 prior to doing an
update of the associated message center. This prevents the CAN module from
transmitting the data while the microcontroller is updating it. Once the
microcontroller has finished configuring the message center, software must clear
TIH = 0 and set MSRDY=MTRQ =DTUP =1, to enable the CAN module to
transmit the data.
The CAN module will not clear the DTUP after the transmission, but the
microcontroller can verify that the transmission has been completed, by
checking the MTRQ bit, which will be cleared (MTRQ = 0) after the
transmission has been successfully completed.
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