18F8680 datasheet(298/496 Pages) MICROCHIP

298 / 496 page

PIC18F6585/8585/6680/8680

DS30491C-page 296

 2004 Microchip Technology Inc.

≤ n ≤ 1, 0 ≤ m ≤ 7]

EXAMPLE 23-5:

READING A CAN MESSAGE

R-x

RXBnDm7 RXBnDm6 RXBnDm5 RXBnDm4 RXBnDm3 RXBnDm2 RXBnDm1 RXBnDm0

bit 7

bit 0

bit 7-0

RXBnDm7:RXBnDm0: Receive Buffer n Data Field Byte m bits (where 0

≤ n < 1 and 0 < m < 7)

Each receive buffer has an array of registers. For example, Receive Buffer 0 has 8 registers:

RXB0D0 to RXB0D7.

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

R-0

REC7

REC6

REC5

REC4

REC3

REC2

REC1

REC0

bit 7

bit 0

bit 7-0

REC7:REC0: Receive Error Counter bits

This register contains the receive error value as defined by the CAN specifications.

When RXERRCNT > 127, the module will go into an error-passive state. RXERRCNT does not

have the ability to put the module in “bus-off” state.

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

; Need to read a pending message from RXB0 buffer.

; To receive any message, filter, mask and RXM1:RXM0 bits in RXB0CON registers must be

; programmed correctly.

;

; Make sure that there is a message pending in RXB0.

BTFSS

RXB0CON, RXFUL

; Does RXB0 contain a message?

BRA

NoMessage

; No.

Handle this situation...

; We have verified that a message is pending in RXB0 buffer.

; If this buffer can receive both Standard or Extended Identifier messages,

; identify type of message received.

BTFSS

RXB0SIDL, EXID

; Is this Extended Identifier?

BRA

StandardMessage

; No.

This is Standard Identifier message.

; Yes.

This is Extended Identifier message.

; Read all 29-bits of Extended Identifier message.

...

; Now read all data bytes

MOVFF

RXB0DO, MY_DATA_BYTE1

...

; Once entire message is read, mark the RXB0 that it is read and no longer FULL.

BCF

RXB0CON, RXFUL

; This will allow CAN Module to load new messages

; into this buffer.

...

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