NEC V850E/PH2 User Manual page 757

(5) Recovery from bus-off state
When the CAN module is in the bus-off state, the CAN module permanently sets its output signals
(CTXDn) to recessive level.
The CAN module recovers from the bus-off state in the following bus-off recovery sequence.
<1> A request to enter the CAN initialization mode
<2> 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 from bus-off state through normal recovery sequence
The CAN module first issues a request to enter the initialization mode (refer too timing <1> in Fig-
ure 18-17, "Recovery from bus-off state through normal recovery sequence," on page 758). This
request will be immediately acknowledged, and the OPMODE bits of the CnCTRL. 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 opera-
tion of the CAN module can be performed by clearing the GOM bit to 0.
Next, the module requests to change the mode from the initialization mode to an operation mode
(refer to timing <2> in Figure 18-17). 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 <3> in Figure 18-17), 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
CnCTRL register.
During the bus-off period and bus-off recovery sequence, the BOFF bit of the CnINFO 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].
Caution: 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 recov-
ery 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 dur-
ing bus-off, the sleep mode will be left and the bus-off recovery sequence will start.
Chapter 18 AFCAN Controller
User's Manual U16580EE3V1UD00 757