DS80C390 datasheet(49/155 Pages) DALLAS

49 / 155 page

DS80C390 High-Speed Microcontroller User’s Guide Supplement

49 of 155

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.

DTUP

Bit 0

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.

DS80C390 Datasheet(PDF) 49 Page - Dallas Semiconductor

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