ECAN1000 User’s Manual
17
BDM-610020026 rev B
The CAN bus controller
The SJA1000 CAN bus controller uses a 16 MHz base oscillator. This
must be taken into account when performing settings in the CAN bus tim-
ing registers that set the baud rate and sampling times of the CAN net-
work.
The SJA1000 CAN controller consists of seven functional blocks. The
host interface logic; the Transmit Buffer; the Receive Buffer; the Accep-
tance Filter; the Bit Stream Processor; the Bit Timing Logic and the Error
management logic. A detailed description of these blocks is listed in the
detailed component specific datasheet reprinted from Philips Semicon-
ductors.
The SJA1000 internal message FIFO RAM provides storage for 64 mes-
sage bytes. Each message can vary from one to up to 8 bytes in length.
Each message object has a unique identifier and can be configured to ei-
ther transmit or to receive.
Each message identifier contains control and status bits. A message ob-
ject with a direction set for receive will send a remote frame by requesting
a message transmission. A message set as transmit will be configured to
automatically send a data frame whenever a remote frame with a match-
ing identifier is received over the CAN bus. All message objects have
separate transmit and receive interrupts and status bits, allowing the CPU
full flexibility in detecting when a remote frame has been sent or received.
The SJA1000 also features masking for acceptance filtering. This feature
allows the user to globally mask, or "don't care", any identifier bits of the
incoming message. This mask is programmable to allow the user to de-
sign an application specifically message identification strategy. There are
separate global masks for standard and extended frames. The incoming
message first passes through the global mask and is then matched to the
identifiers in the message objects