ST STM32F101 Series Reference Manual page 304

Controller area network (bxCAN)
Bit 1 RTR: Remote Transmission Request
0: Data frame
1: Remote frame
Bit 0 TXRQ: Transmit Mailbox Request
Set by software to request the transmission for the corresponding mailbox.
Cleared by hardware when the mailbox becomes empty.
Mailbox data length control and time stamp register (CAN_TDTxR) (x=0..2)
All bits of this register are write protected when the mailbox is not in empty state.
Address offsets: 0x184, 0x194, 0x1A4
Reset value: 0xXX where X is undefined
31 30 29
rw rw rw
15 14 13
Reserved
Bits 31:16 TIME[15:0]: Message Time Stamp
This field contains the 16-bit timer value captured at the SOF transmission.
Bits 15:9 Reserved
Bit 8 TGT: Transmit Global Time
This bit is active only when the hardware is in the Time Trigger Communication mode, TTCM bit of
the CAN_MCR register is set.
0: Time stamp TIME[15:0] is not sent.
1: Time stamp TIME[15:0] value is sent in the last two data bytes of the 8-byte message: TIME[7:0]
in data byte 6 and TIME[15:8] in data byte 7, replacing the data written in CAN_TDHxR[31:16]
register (DATA6[7:0] and DATA7[7:0]). DLC must be programmed as 8 in order these two bytes to
be sent over the CAN bus.
Bits 7:4 Reserved
Bits 3:0 DLC[3:0]: Data Length Code
This field defines the number of data bytes a data frame contains or a remote frame request.
A message can contain from 0 to 8 data bytes, depending on the value in the DLC field.
304/501
28 27 26 25
rw rw rw rw
12 11 10 9
24 23 22 21
TIME[15:0]
rw rw rw rw
8 7 6 5
TGT Reserved
rw
20 19 18 17
rw rw rw rw
4 3 2 1
DLC[3:0]
rw rw rw
RM0008
16
rw
0
rw