Download 82C900 User`s Manual

82C900
Standalone TwinCAN Controller
TwinCAN Module Description
3.2
TwinCAN Control Shell
3.2.1
Initialization Processing
After an external hardware reset or the occurrence of a “bus-off” event, the respective
CAN controller node is logically disconnected from the associated CAN bus and does
not participate in any message transfer. The “Disconnect Mode” is indicated by the ACR/
BCR control register bit INIT = 1, which is automatically set in case of a reset or “bus-off”
event. Furthermore, the “Disconnect Mode” can be also entered by setting bit INIT to 1
via software. While INIT is active, all message transfers between the affected TwinCAN
node controller and its associated CAN bus are stopped and the bus output pin (TXDC)
is held on ‘High’ level (recessive state).
After an external hardware reset, all control and message object registers are reset to
their associated reset values. Upon an activation of the “bus-off” state or a write access
to register ACR/BCR with INIT = 1, all respective control and message object registers
hold their current values (except the error counters).
Resetting bit INIT to 0 without being in “bus-off” state starts a connect procedure, which
must monitor at least one “Bus Idle” event (11 consecutive ‘recessive’ bits) on the
associated CAN bus before the node is allowed to take part in CAN traffic again.
During the bus-off recovery sequence:
• The Receive and Transmit Error Counter within the Error Handling Control Logic are
reset.
• 128 “Bus Idle” events (11 consecutive ‘recessive’ bits) must be detected, before the
reconnect procedure can be initiated. The monitoring of the bus idle events is
immediately started by hardware after entering the “bus-off” state. The number of “Bus
Idle” events already detected is counted and indicated by the receive error counter.
• The reconnect procedure tests bit INIT by hardware after 128 “Bus Idle” events. If INIT
is still set, the affected TwinCAN node controller waits until INIT is cleared and at least
one “Bus Idle” event is detected on the CAN bus, before the node takes part in CAN
traffic again. If INIT has been already cleared, the message transfer between the
affected TwinCAN node controller and its associated CAN bus is immediately
enabled.
User’s Manual
3-4
V1.0D2, 2000-12