COP685BC datasheet(22/57 Pages) NSC

22 / 57 page

CAN Interface Block (Continued)

Fully automatic transmission on error is supported for mes-

sages not longer than two bytes. Messages which are longer

than two bytes have to be processed by software.

The interface is compatible with CAN Specification 2.0 part

B, without the capability to receive/transmit extended

frames. Extended frames on the bus are checked and ac-

knowledged according to the CAN specification.

The maximum bus speed achievable with the CAN interface

is a function of crystal frequency, message length and soft-

ware overhead. The device can support a bus speed of up to

1 Mbit/s with a 10 MHz oscillator and 2 byte messages. The

1 Mbit/s bus speed refers to the rate at which protocol and

data bits are transferred on the bus. Longer messages re-

quire slower bus speeds due to the time required for soft-

ware intervention between data bytes. The device will sup-

port a maximum of 125k bit/s with eight byte messages and

a 10 MHz oscillator.

Functional Block Description of

the CAN Interface

Interface Management Logic (IML)

The IML executes the CPU’s transmission and reception

commands and controls the data transfer between CPU,

Rx/Tx and CAN registers. It provides the CAN Interface with

Rx/Tx data from the memory mapped Register Block. It also

sets and resets the CAN status information and generates

interrupts to the CPU.

Bit Stream Processor (BSP)

The BSP is a sequencer controlling the data stream between

The Interface Management Logic (parallel data) and the bus

line (serial data). It controls the transceive logic with regard

to reception and arbitration, and creates error signals ac-

cording to the bus specification

DS012067-49

FIGURE 17. CAN Interface Block Diagram

COP685BC Datasheet(PDF) 22 Page - National Semiconductor (TI)