MCP2510-EST datasheet(6/76 Pages) MICROCHIP

6 / 76 page

MCP2510

DS21291C-page 6

Preliminary

 2000 Microchip Technology Inc.

1.3

CAN Protocol Engine

The CAN protocol engine combines several functional

blocks, shown in Figure 1-4. These blocks and their

functions are described below.

1.4

Protocol Finite State Machine

The heart of the engine is the Finite State Machine

(FSM). This state machine sequences through mes-

sages on a bit by bit basis, changing states as the fields

of the various frame types are transmitted or received.

The FSM is a sequencer controlling the sequential data

stream between the TX/RX Shift Register, the CRC Reg-

ister, and the bus line. The FSM also controls the Error

Management Logic (EML) and the parallel data stream

between the TX/RX Shift Registers and the buffers. The

FSM insures that the processes of reception, arbitration,

transmission, and error signaling are performed accord-

ing to the CAN protocol. The automatic retransmission of

messages on the bus line is also handled by the FSM.

1.5

Cyclic Redundancy Check

The Cyclic Redundancy Check Register generates the

Cyclic Redundancy Check (CRC) code which is trans-

mitted after either the Control Field (for messages with

0 data bytes) or the Data Field, and is used to check the

CRC field of incoming messages.

1.6

Error Management Logic

The Error Management Logic is responsible for the fault

confinement of the CAN device. Its two counters, the

Receive Error Counter (REC) and the Transmit Error

Counter (TEC), are incremented and decremented by

commands from the Bit Stream Processor. According to

the values of the error counters, the CAN controller is set

into the states error-active, error-passive or bus-off.

1.7

Bit Timing Logic

The Bit Timing Logic (BTL) monitors the bus line input

and handles the bus related bit timing according to the

CAN protocol. The BTL synchronizes on a recessive to

dominant bus transition at Start of Frame (hard syn-

chronization) and on any further recessive to dominant

bus line transition if the CAN controller itself does not

transmit a dominant bit (resynchronization). The BTL

also provides programmable time segments to com-

pensate for the propagation delay time, phase shifts,

and to define the position of the Sample Point within the

bit time. The programming of the BTL depends upon

the baud rate and external physical delay times.

FIGURE 1-4:

CAN Protocol Engine Block Diagram

Bit Timing Logic

CRC<14:0>

Comparator

Receive<7:0>

Transmit<7:0>

Sample<2:0>

Majority

Decision

StuffReg<5:0>

Comparator

Transmit Logic

Receive

Error Counter

Transmit

Error Counter

Protocol

FSM

SAM

BusMon

Rec/Trm Addr.

RecData<7:0>

TrmData<7:0>

Shift<14:0>

(Transmit<5:0>, Receive<7:0>)

REC

TEC

ErrPas

BusOff

Interface to Standard Buffer

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