4

AT90CAN128

4330B–CAN–03/04

Figure 2. Component Placement

Utilising CAN-

Transceiver Extra-

features

Many CAN transceiver devices available have various extra functions accessible

through pins 5 and 8. The ATADAPCAN01 allows you to take advantage of some of

these features. Pin 8 on both "CAN1" and "CAN2" footprints are connected centre pin of

the "SLOPE CTRL" connector. Pin 5 of "CAN1" is connected to the centre-tap of the ter-

mination network, and pin 5 of "CAN2" is connected to R6 and C2 as shown in Figure 2.

Slope Control (pin 8,

"CAN1" and "CAN2")

CAN transceivers supporting slope or slew-rate control allow a resistor to be connected

between the RS pin (pin 8) and ground to limit the slope of the bus-driving signal. This

reduced EMI emmissions while restricting the maximum transmission rate. Pin 8 on both

"CAN1" and "CAN2" devices are connected to the centre pin of the "SLOPE CTRL"

jumper. Setting the jumper to the ON position, connects the centre pin to ground through

resistor R7, while setting it to the OFF position connects the centre pin directly to ground

(for no slope control, or high-speed mode). Refer to the CAN transceiver device docu-

mentation for information on selecting the value of R7 (24k by default).

Standby Function (pin 8,

"CAN1" and "CAN2")

On some CAN transceivers, pin 8 can be driven by a logic level to switch the transceiver

into standby mode. The centre pin of the "SLOPE CTRL" header (with the jumper

removed) can be connected to an I/O pin on the AVR device for this purpose. Your AVR

code should drive this signal as specified in the CAN transceiver documentation.

Shutdown Function

(pin 5, "CAN2")

Some CAN transceivers have a SHUTDOWN function which is configured by an R-C

connection on pin 5. Pin 5 of the "CAN2" footprint is connected to resistor R6 to Vcc and

capacitor C2 to ground, as shown in the schematic diagram. By default R6 is a 0 ohm

connection to Vcc and C2 is not mounted. Both parts are 0603 size. Consult the CAN

transceiver documentation for further information.

Split Voltage (pin 5,

"CAN1")

The centre-point of the CAN bus termination (if enabled) can be stabilised by connecting

it to pin 5 of certain CAN transceivers. If the CAN transceiver supports this feature, a 0

ohm 0603 resistor can be mounted in R14, with the "SPLIT" and "TERM" jumpers set

accordingly (see Section ”CAN bus termination”).