RXB0D2 datasheet(66/92 Pages) MICROCHIP

66 / 92 page

MCP2515

DS21801G-page 66

 2003-2012 Microchip Technology Inc.

Each status bit returned in this command may also be

read by using the standard Read command with the

appropriate register address.

12.9

RX STATUS

Instruction

The RX STATUS instruction (Figure 12-9) is used to

quickly determine which filter matched the message

and message type (standard, extended, remote). After

the command byte is sent, the controller will return

8 bits of data that contain the status data. If more clocks

are sent after the eight bits are transmitted, the

controller will continue to output the same status bits as

long as the CS pin stays low and clocks are provided.

12.10 BIT MODIFY Instruction

The BIT MODIFY instruction provides a means for set-

ting or clearing individual bits in specific status and con-

trol registers. This command is not available for all

registers. See Section 11.0 “Register Map” to

determine which registers allow the use of this

command.

The part is selected by lowering the CS pin and the Bit

Modify command byte is then sent to the MCP2515.

The command is followed by the address of the

The mask byte determines which bits in the register will

be allowed to change. A ‘1’ in the mask byte will allow

a bit in the register to change, while a ‘0’ will not.

The data byte determines what value the modified bits

in the register will be changed to. A ‘1’ in the data byte

will set the bit and a ‘0’ will clear the bit, provided that

the mask for that bit is set to a ‘1’ (see Figure 12-7).

FIGURE 12-1:

BIT MODIFY

TABLE 12-1:

SPI INSTRUCTION SET

Note:

Executing the Bit Modify command on

registers that are not bit-modifiable will

force the mask to FFh. This will allow byte-

writes to the registers, not bit modify.

Mask byte

Data byte

Contents

Resulting

Contents

00 1

XX 1

01 0

01 1

Instruction Name

Instruction Format

Description

RESET

1100 0000

Resets internal registers to default state, set Configuration mode.

READ

0000 0011

Read data from register beginning at selected address.

READ RX BUFFER

1001 0nm0

When reading a receive buffer, reduces the overhead of a normal

Read command by placing the Address Pointer at one of four

locations, as indicated by ‘n,m’. Note: The associated RX flag bit

(CANINTF.RXnIF) will be cleared after bringing CS high.

WRITE

0000 0010

Write data to register beginning at selected address.

LOAD TX BUFFER

0100 0abc

When loading a transmit buffer, reduces the overhead of a normal

Write command by placing the Address Pointer at one of six

locations as indicated by ‘a,b,c’.

RTS

(Message

Request-To-Send)

1000 0nnn

Instructs controller to begin message transmission sequence for

any of the transmit buffers.

READ STATUS

1010 0000

Quick polling command that reads several status bits for transmit

and receive functions.

RX STATUS

1011 0000

Quick polling command that indicates filter match and message

type (standard, extended and/or remote) of received message.

BIT MODIFY

0000 0101

Allows the user to set or clear individual bits in a particular

command. Executing this command on registers that are not bit-

modifiable will force the mask to FFh. See the register map in

Section 11.0 “Register Map” for a list of the registers that apply.

1000 0nnn

Request-to-send for TXBO

Request-to-send for TXB1

Request-to-send for TXB2

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