upd70f3402 Renesas Electronics Corporation., upd70f3402 Datasheet - Page 544

• Manufacturer Part Number: upd70f3402
• Description: 32-/16-bit Single-chip Microcontroller With Can Interface
• Manufacturer: Renesas Electronics Corporation.

(5)
Caution:
Remark:
544
Recovery from bus-off state
When the CAN module is in the bus-off state, the transmission pins (CTXDn) cut off from the CAN
bus always
output the recessive level.
The CAN module recovers from the bus-off state in the following bus-off recovery sequence.
<1> Request to enter the CAN initialization mode
<2> Request to enter a CAN operation mode
(a) Recovery from bus-off state through normal recovery sequence
The CAN module first issues a request to enter the initialization mode (refer to timing <1> in Figure
16-17). 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
operation 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 16-17). 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 or more. 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 16-17), 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.
Whether the CAN module has entered the 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].
(a)
(b)
In the bus-off recovery sequence, the REC0 to REC6 bits 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 be
released from the bus-off state, the module must enter the initialization mode once. If
the module is in the CAN sleep mode or CAN stop mode, however, it cannot directly
enter the initialization mode. In this case, the bus off recovery sequence is started at
the same time as the CAN sleep mode is released even without shifting to the initial-
ization mode. In addition to clearing the CnCTRL.PSMODE1 and CnCTRL.PSMODE0
bits by software, the bus off recovery sequence is also started due to wake-up by
dominant edge detection on the CAN bus.
n = 0, 1
Recovery operation through normal recovery sequence
Forced recovery operation that skips recovery sequence
Chapter 16 FCAN Controller
User’s Manual U16702EE3V2UD00