C8051F040/1/2/3/4/5/6/7

226 Rev. 1.5

C8051F040/1/2/3/4/5/6/7

Rev. 1.5 227

18. Controller Area Network (CAN0)

IMPORTANT DOCUMENTATION NOTE: The Bosch CAN Controller is integrated in the C8051F04x Fam-

ily of devices. This section of the data sheet gives a description of the CAN controller as an overview and

offers a description of how the Silicon Labs CIP-51 MCU interfaces with the on-chip Bosch CAN controller.

In order to use the CAN controller, please refer to Bosch’s C_CAN User’s Manual (revision 1.2) as an

accompanying manual to Silicon Labs’ C8051F04x Data sheet.

The C8051F04x family of devices feature a Control Area Network (CAN) controller that enables serial com-

munication using the CAN protocol. Silicon Labs CAN facilitates communication on a CAN network in

accordance with the Bosch specification 2.0A (basic CAN) and 2.0B (full CAN). The CAN controller con-

sists of a CAN Core, Message RAM (separate from the CIP-51 RAM), a message handler state machine,

and control registers. Silicon Labs CAN is a protocol controller and does not provide physical layer drivers

(i.e., transceivers). Figure 18.1 shows an example typical configuration on a CAN bus.

Silicon Labs CAN operates at bit rates of up to 1 Mbit/second, though this can be limited by the physical

layer chosen to transmit data on the CAN bus. The CAN processor has 32 Message Objects that can be

configured to transmit or receive data. Incoming data, message objects and their identifier masks are

stored in the CAN message RAM. All protocol functions for transmission of data and acceptance filtering is

performed by the CAN controller and not by the CIP-51 MCU. In this way, minimal CPU bandwidth is

needed to use CAN communication. The CIP-51 configures the CAN controller, accesses received data,

and passes data for transmission via Special Function Registers (SFRs) in the CIP-51.

Figure 18.1. Typical CAN Bus Configuration

C8051F04x

CANTX

CANRX

CAN_H

CAN_L

Isolation/Buffer (Optional)

CAN

Transceiver

Isolation/Buffer (Optional)

CAN

Transceiver

Isolation/Buffer (Optional)

CAN

Transceiver

CAN Protocol Device CAN Protocol Device

C8051F040/1/2/3/4/5/6/7

228 Rev. 1.5

18.1. Bosch CAN Controller Operation

The CAN Controller featured in the C8051F04x family of devices is a full implementation of Bosch’s full

CAN module and fully complies with CAN specification 2.0B. A block diagram of the CAN controller is

shown in Figure 18.2. The CAN Core provides shifting (CANTX and CANRX), serial/parallel conversion of

messages, and other protocol related tasks such as transmission of data and acceptance filtering. The

message RAM stores 32 message objects which can be received or transmitted on a CAN network. The

CAN registers and message handler provide an interface for data transfer and notification between the

CAN controller and the CIP-51.

The function and use of the CAN Controller is detailed in the Bosch CAN User’s Guide. The User’s Guide

should be used as a reference to configure and use the CAN controller. This Silicon Labs data sheet

describes how to access the CAN controller.

The CAN Controller is typically initialized using the following steps:

Step 1. Set the SFRPAGE register to CAN0_PAGE.

Step 2. Set the INIT the CCE bits to ‘1’ in the CAN0CN Register. See the CAN User’s Guide for bit

definitions.

Step 3. Set timing parameters in the Bit Timing Register and the BRP Extension Register.

Step 4. Initialize each message object or set it’s MsgVal bit to NOT VALID.

Step 5. Reset the INIT bit to ‘0’.

The CAN Control Register (CAN0CN), CAN Test Register (CAN0TST), and CAN Status Register

(CAN0STA) in the CAN controller can be accessed directly or indirectly via CIP-51 SFR’s. All other CAN

registers must be accessed via an indirect indexing method described in Section “18.2.5. Using

CAN0ADR, CAN0DATH, and CANDATL to Access CAN Registers” on page 232.

Figure 18.2. CAN Controller Diagram

Message Handler

REGISTERS

Message RAM

(32 Message Objects)

CAN

Core

TX RX

CAN Controller

CIP-51

MCU

Interrupt

CANTX

CANRX

C8051F04x

CAN_CLK

sys

)

BRP

Prescaler

Part #	C8051F041-GQ
Description	MCU 8BIT CISC 64KB FLASH 3V 64TQFP - Trays
Category	IC
Availability	In Stock
Qty	2

C8051F041-GQ

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