Intel 8XC196K Series User Manual page 306

CAN_MSG x CON1 (Continued)
x = 1–15 (87C196CA)
The CAN message object x control 1 (CAN_MSG x CON1) register indicates whether a message
object has been updated, whether a message has been overwritten, whether the CPU is updating the
message, and whether a transmission or reception is pending.
This register consists of four bit-pairs — the most-significant bit of each pair is in true form and the
least-significant bit is in complement form. This format allows software to set or clear any bit with a
single write operation, without affecting the remaining bits.
7
87C196CA
RMTPND
Bit Bit
Number Mnemonic
3:2 MSGLST or
CPUUPD
1:0 NEWDAT
Figure 12-15. CAN Message Object x Control 1 (CAN_MSG x CON1) Register (Continued)
CAN SERIAL COMMUNICATIONS CONTROLLER
RMTPND TX_REQ TX_REQ
Message Lost (receive)
For a receive message object, the CAN controller sets this bit-pair to
indicate that it stored a new message while the NEWDAT bit-pair was still
set, overwriting the previous message.
bit 3 bit 2
0 1 no overwrite occurred
1 0 a message was lost (overwritten)
CPU Updating (transmit)
For a transmit message object, software should set this bit-pair to indicate
that it is in the process of updating the message contents. This prevents a
remote frame from triggering a transmission that would contain invalid
data.
bit 3 bit 2
0 1 the message is valid
1 0 software is updating data
New Data
This bit-pair indicates whether a message object is valid (configured and
ready for transmission).
bit 1 bit 2
0 1 not ready
1 0 message object is valid
For receive message objects, the CAN peripheral sets this bit-pair when it
stores new data into the message object.
For transmit message objects, set this bit-pair and clear the CPUUPD bit-
pair to indicate that the message contents have been updated. Clearing
CPUUPD prevents a remote frame from triggering a transmission that
would contain invalid data.
During initialization, clear this bit for any unused message objects.
Address: 1E x 1H ( x = 1–F)
Reset State: Unchanged
MSGLST MSGLST
NEWDAT
CPUUPD CPUUPD
Function
0
NEWDAT
12-27