RL78/D1A User's Manual: Hardware - Renesas

Under development
Preliminary document
Specifications in this document are tentative and subject to change.
RL78/D1A CHAPTER 14 CAN CONTROLLER
14.10.3 Automatic block transmission (ABT)
The automatic block transmission (ABT) function is used to transmit two or more data frames successively with no CPU
interaction. The maximum number of transmit message buffers assigned to the ABT function is eight (message buffer
numbers 0 to 7).
By setting OPMODE [2:0] bits of the C0CTRL register to 010B, "normal operation mode with automatic block
transmission function" (hereafter referred to as ABT mode) can be selected.
To issue an ABT transmission request, define the message buffers by software first. Set the MA0 bit (1) in all the
message buffers used for ABT, and define all the buffers as transmit message buffers by setting MT [2:0] bits to 000B. Be
sure to set the ID for each message buffer for ABT even when the same ID is being used for all the message buffers. To
use two or more IDs, set the ID of each message buffer by using the C0MIDLm and C0MIDHm registers. Set the
C0MDLCm and C0MDATA0m to C0MDATA7m registers before issuing a transmission request for the ABT function.
After initialization of message buffers for ABT is finished, the RDY bit needs to be set (1). In the ABT mode, the TRQ
bit does not have to be manipulated by software.
After the data for the ABT message buffers has been prepared, set the ABTTRG bit to 1. Automatic block transmission
is then started. When ABT is started, the TRQ bit in the first message buffer (message buffer 0) is automatically set to 1.
After transmission of the data of message buffer 0 has finished, TRQ bit of the next message buffer, message buffer 1, is
set automatically. In this way, transmission is executed successively.
A delay time can be inserted by program in the interval in which the transmission request (TRQ) is automatically set
while successive transmission is being executed. The delay time to be inserted is defined by the C0GMABTD register.
The unit of the delay time is DBT (data bit time). DBT depends on the setting of the C0BRP and C0BTR registers.
Among transmit objects within the ABT-area, the priority of the transmission ID is not evaluated. The data of message
buffers 0 to 7 are sequentially transmitted. When transmission of the data frame from message buffer 7 has been
completed, the ABTTRG bit is automatically cleared to 0 and the ABT operation is finished.
If the RDY bit of an ABT message buffer is cleared during ABT, no data frame is transmitted from that buffer, ABT is
stopped, and the ABTTRG bit is cleared. After that, transmission can be resumed from the message buffer where ABT
stopped, by setting the RDY and ABTTRG bits to 1 by software. To not resume transmission from the message buffer
where ABT stopped, the internal ABT engine can be reset by setting the ABTCLR bit to 1 while ABT mode is stopped and
ABTTRG bit is cleared to 0. In this case, transmission is started from message buffer 0 if the ABTCLR bit is cleared to 0
and then the ABTTRG bit is set to 1.
An interrupt can be used to check if data frames have been transmitted from all the message buffers for ABT. To do so,
the IE bit of the C0MCTRLm register of each message buffer except the last message buffer needs to be cleared (0).
If a transmit message buffer other than those used by the ABT function (message buffer 8 to 15) is assigned to a
transmit message buffer, the message to be transmitted next is determined by the priority of the transmission ID of the
ABT message buffer whose transmission is currently held pending and the transmission ID of the message buffers other
than those used by the ABT function.
Transmission of a data frame from an ABT message buffer is not recorded in the transmit history list (THL).
R01UH0317EJ0004 Rev. 0.04 897
Feb. 22, 2013