COP888EB datasheet(22/75 Pages) NSC

22 / 75 page

CAN Interface Block

This device supports applications which require a low speed

CAN interface. It is designed to be programmed with two

transmit and two receive registers. The user’s program may

check the status bytes in order to get information of the bus

state and the received or transmitted messages. The device

has the capability to generate an interrupt as soon as one

byte has been transmitted or received. Care must be taken if

more than two bytes in a message frame are to be

transmitted/received. In this case the user’s program must

poll the transmit buffer empty (TBE)/receive buffer full (RBF)

bits or enable their respective interrupts and perform a data

exchange between the user data and the Tx/Rx registers.

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.

DS012837-16

FIGURE 14. CAN Interface Block Diagram

COP888EB Datasheet(PDF) 22 Page - National Semiconductor (TI)