upd70f3402 Renesas Electronics Corporation., upd70f3402 Datasheet - Page 649

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

In the receive-only mode, no message frames can be transmitted from the CAN module to the CAN
bus. Transmit requests issued for message buffers defined as transmit message buffers are held pend-
ing.
In the receive-only mode, the CAN transmission pin (CTXDn) in the CAN module is fixed to the reces-
sive level. Therefore, no active error flag can be transmitted from the CAN module to the CAN bus even
when a CAN bus error is detected while receiving a message frame. Since no transmission can be
issued from the CAN module, the transmission error counter TEC is never updated. Therefore, a CAN
module in the receive-only mode does not enter the bus-off state.
Furthermore, ACK is not returned to the CAN bus in this mode upon the valid reception of a message
frame. Internally, the local node recognizes that it has transmitted ACK. An overload frame cannot be
transmitted to the CAN bus.
Caution:
16.13.2 Single-shot mode
In the single-shot mode, automatic re-transmission as defined in the CAN protocol is switched off.
(According to the CAN protocol, a message frame transmission that has been aborted by either arbitra-
tion loss or error occurrence has to be repeated without control by software.) All other behaviour of sin-
gle shot mode is identical to normal operation mode. Features of single shot mode can not be used in
combination with normal mode with ABT.
The single-shot mode disables the re-transmission of an aborted message frame transmission accord-
ing to the setting of the AL bit of the CnCTRL register. When the AL bit is cleared to 0, re-transmission
upon arbitration loss and upon error occurrence is disabled. If the AL bit is set to 1, re-transmission
upon error occurrence is disabled, but re-transmission upon arbitration loss is enabled. As a conse-
quence, the TRQ bit in a message buffer defined as a transmit message buffer is cleared to 0 by the fol-
lowing events.
The events arbitration loss and error occurrence can be distinguished by checking the CINTS4 and
CINTS3 bits of the CnINTS register, and the type of the error can be identified by reading the LEC[2:0]
bits of the CnLEC register.
Upon successful transmission of the message frame, the transmit completion interrupt bit CINTS0 of
the CnINTS register is set to 1. If the CIE0 bit of the CnIE register is set to 1 at this time, an interrupt
request signal is output.
The single-shot mode can be used when emulating time-triggered communication methods (e.g.,
TTCAN level 1).
Caution:
• Successful transmission of the message frame
• Arbitration loss while sending the message frame (AL bit = 0)
• Error occurrence while sending the message frame
If only two CAN nodes are connected to the CAN bus and one of them is operating in
the receive-only mode, there is no ACK on the CAN bus. Due to the missing ACK, the
transmitting node will transmit an active error flag, and repeat transmitting a mes-
sage frame. The transmitting node becomes error passive after transmitting the mes-
sage frame 16 times (assuming that the error counter was 0 in the beginning and no
other errors have occurred). When the message frame is transmitted for the 17th
time, the transmitting node generates a passive error flag. The receiving node in the
receive-only mode detects the first valid message frame at this point, and the VALID
bit is set to 1 for the first time.
The AL bit is only valid in single-shot mode. It does not affect the operation of re-
transmission upon arbitration loss in other operation modes.
User’s Manual U16702EE3V2UD00
Chapter 16 FCAN Controller
649