3

AT90CAN128

4330B–CAN–03/04

CAN Bus Interface

Several options are available to physically connect the ATADAPCAN01 to a CAN bus.

BUS Connectors

The D-SUB-9 MALE connector is the primary connection point to a CAN bus. Alterna-

tively, the 10-pin header labelled "CAN BUS flat-cable" can be used, or both connectors

can be used if the CAN bus topology requires it. Both connectors are wired according to

CiA Draft Standard 102 version 2.0 as shown in table 1.

Table 1. CAN Bus Connector Wiring

Note:

1. CAN_SHLD pins are not connected together internally

CAN BUS Grounding and

Shielding

The "CAN_SHLD" signal in each of the two CAN bus connectors can be optionally con-

nected to ground by mounting 0 ohm or small value resistors in positions R2 (for D-SUB-

9) and R3 (for flat-cable). The landing pads of both R2 and R3 are 1206 standard size.

By default, the "CAN_GND" signals in both connectors are wired to the STK500 ground

through 0 ohm resistor R1. Removing R1 will isolate the "CAN_GND" ground signals on

the CAN bus from the STK500 / ATADAPCAN01 ground.

CAN BUS Termination

To function correctly, a CAN bus requires 120 ohm termination on both ends. The

ATADAPCAN01 can become a terminated node on the CAN bus simply by setting the

jumper labelled "TERM". This terminates the CAN bus with two series-connected 62

ohm resistors. Setting the jumper labelled "SPLIT" connects the centre-tap between

these two resistors to ground through 10nF capacitor C1. This reduces common-mode

noise on the bus line. This centre tap can also be stabilised as described later in the

”Split voltage” section (if supported by the CAN transceiver mounted in "CAN1").

evaluation of alternate CAN devices as well as to provide access to various extra fea-

tures of some of these parts. Refer to the schematic diagram in Figure 2 (below) while

considering these options.

Both "CAN1" and "CAN2" footprints use standard CAN device pinouts for pins 1, 2, 3, 4,

6 and 7. By default, "CAN1" is mounted on the board (Atmel ATA6660). To use a device

in "CAN2", solder the device to the board, and remove the 0 ohm ’resistors’ labelled R8,

R9 R10 from the "CAN1" section, and mount them into the "CAN2" section in positions

R11, R12, R13. Although it is acceptable that idle CAN transceivers remain attached to

the CAN bus, only one CAN device should be connected to the AVR device at any time.

Signal Description

D-SUB-9 pin

Flat-cable Pin

Reserved

1

1

CAN_L

2

3

CAN_GND

3

5

Reserved

4

7

CAN_SHLD*

CAN_GND

6

2

CAN_H

7

4

Reserved

8

6

CAN_V+

9

8

(not used)

10