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
(5) Recovery from bus-off state
When the CAN module is in the bus-off state, the CAN module permanently sets its output signals (CTxD) to
recessive level.
The CAN module recovers from the bus-off state in the following bus-off recovery sequence.
A request to enter the CAN initialization mode
A request to enter a CAN operation mode
(a) Recovery operation through normal recovery sequence
(b) Forced recovery operation that skips recovery sequence
(a) Recovery operation from bus-off state through normal recovery sequence
The CAN module first issues a request to enter the initialization mode (refer to timing in Figure 14-17).
This request will be immediately acknowledged, and the OPMODE bits of the C0CTRL, C1CTRL register are
cleared to 000B. Processing such as analyzing the fault that has caused the bus-off state, re-defining the
CAN module and message buffer using application software, or stopping the operation of the CAN module
can be performed by clearing the GOM bit to 0.
Next, the user requests to change the mode from the initialization mode to an operation mode (refer to timing
in Figure 14-17). This starts an operation to recover the CAN module from the bus-off state. The
conditions under which the module can recover from the bus-off state are defined by the CAN protocol ISO
11898, and it is necessary to detect 11 consecutive recessive-level bits 128 times. At this time, the request to
change the mode to an operation mode is held pending until the recovery conditions are satisfied. When the
recovery conditions are satisfied (refer to timing in Figure 14-17), the CAN module can enter the
operation mode it has requested. Until the CAN module enters this operation mode, it stays in the
initialization mode. Completion to be requested operation mode can be confirmed by reading the OPMODE
bits of the C0CTRL, C1CTRL register.
During the bus-off period and bus-off recovery sequence, the BOFF bit of the C0INFO, C1INFO register stays
set (to 1). In the bus-off recovery sequence, the reception error counter (REC[6:0]) counts the number of
times 11 consecutive recessive-level bits have been detected on the bus. Therefore, the recovery state can
be checked by reading REC[6:0].
Cautions 1. If the Bus-off Recovery Sequence is interrupted by entering Initialization Mode and re-entering
any Operation Mode, the Bus-off Recovery Sequence will restart from the beginning, and the
waiting phase will be again 128 times 11 recessive-level bits, counted from this point.
2. In the bus-off recovery sequence, REC [6:0] counts up (+1) each time 11 consecutive
recessive-level bits have been detected. Even during the bus-off period, the CAN
module can enter the CAN sleep mode or CAN stop mode. To start the bus-off recovery
sequence, it is necessary to transit to the initialization mode once.
However, when the CAN module is in either CAN sleep mode or CAN stop mode,
transition request to the initialization mode is not accepted, thus you have to release
the CAN sleep mode first. In this case, as soon as the CAN sleep mode is released, the
bus-off recovery sequence starts and no transition to initialization mode is necessary.
If the CAN module detects a dominant edge on the CAN bus while in sleep mode even
during bus-off, the sleep mode will be left and the bus-off recovery sequence will start
(In the state that the CAN clock is supplied, it is necessary to clear the PSMODE by
software after dominant edge detection).
R01UH0317EJ0004 Rev. 0.04 802
Feb. 22, 2013