MCP2518FD datasheet(67/96 Pages) MICROCHIP

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 2019 Microchip Technology Inc.

DS20000000A-page 67

MCP2518FD

4.0

SPI INTERFACE

The MCP2518FD device is designed to interface

directly with a Serial Peripheral Interface port available

most

microcontrollers.

The

SPI

the

microcontroller must be configured in mode 0,0 or

1,1 in 8-bit operating mode.

SFR and Message Memory (RAM) are accessed

using SPI instructions. Figure 4-1 illustrates the

generic format of the SPI instructions (SPI mode 0,0).

Each instruction starts with driving nCS low (falling

edge on nCS). The 4-bit command and the 12-bit

address are shifted into SDI on the rising edge of SCK.

During a write instruction, data bits are shifted into SDI

on the rising edge of SCK. During a read instruction,

data bits are shifted out of SDO on the falling edge of

SCK. One or more data bytes are transfered with one

instruction. Data bits are updated on the falling edge of

SCK and must be valid on the rising edge of SCK.

Each instruction ends with driving nCS high (rising

edge on nCS).

Refer to Figure 7-1 for detailed input and output timing

for both mode 0,0 and mode 1,1.

Table 4-1 lists the SPI instructions and their format.

FIGURE 4-1:

SPI INSTRUCTION FORMAT

Note 1: The frequency of SCK has to be less than

or equal to half the frequency of SYSCLK.

This ensures that the synchronization

between SCK and SYSCLK works

correctly.

2: In order to minimize the Sleep current, the

SDO pin of the MCP2518FD device must

not be left floating while the device is in

Sleep mode. This can be achieved by

enabling a pull-up or pull-down resistor

inside the MCU on the pin that is

connected to the SDO pin, while the

MCP2518FD device is in Sleep mode.

TABLE 4-1:

SPI INSTRUCTIONS

Name

Format

Description

RESET

C = 0b0000; A = 0x000 Resets internal registers to default state; selects Configuration mode.

READ

C = 0b0011; A; D = SDO Read SFR/RAM from address A.

WRITE

C = 0b0010; A; D = SDI Write SFR/RAM to address A.

READ_CRC

C = 0b1011; A; N;

D = SDO; CRC = SDO

Read SFR/RAM from address A. N data bytes. Two bytes CRC.

CRC is calculated on C, A, N and D.

WRITE_CRC

C = 0b1010; A; N;

D = SDI; CRC = SDI

Write SFR/RAM to address A. N data bytes. Two bytes CRC.

CRC is calculated on C, A, N and D.

WRITE_SAFE

C = 0b1100; A;

D = SDI; CRC = SDI

Write SFR/RAM to address A. Check CRC before write. CRC is calcu-

lated on C, A and D.

Legend: C = Command (4 bit), A = Address (12 bit), D = Data (1 to n bytes), N = Number of Bytes (1 byte), CRC

(2 bytes)

123

567

910

nCS

SCK

SDI

SDO

C<3>

C<2>

C<1>

C<0>

A<11> A<10>

A<9>

A<8>

A<7>

A<6>

A<5>

A<4>

A<3>

A<2>

A<1>

A<0>

D<7>

D<6>

D<5>

D<4>

D<3>

D<2>

D<1>

D<0>

D<7>

D<6>

D<5>

D<4>

D<3>

D<2>

D<1>

D<0>

Sample

Update

Sample

Update

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