MCP2517FD datasheet(68/98 Pages) MICROCHIP

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MCP2517FD

DS20005688B-page 68

 2017-2018 Microchip Technology Inc.

4.1

SFR Access

The SFR access is byte-oriented. Any number of data

bytes can be read or written with one instruction. The

address is incremented by one automatically after

every data byte. The address rolls over from 0x3FF to

0x000 and from 0xFFF to 0xE00.

The following SPI instructions only show the different

fields and their values. Every instruction follows the

generic format illustrated in Figure 4-1.

4.1.1

RESET

Figure 4-2 illustrates the RESET instruction. The

instruction starts with nCS going low. The Command

(C<3:0> = 0b0000) is followed by the Address

(A<11:0> = 0x000). The instruction ends when nCS

goes high.

The RESET instruction should only be issued after the

device has entered Configuration mode. All SFR and

State Machines are reset just like during a Power-on

Reset (POR), and the device transitions immediately to

Configuration mode.

The Message Memory is not changed.

The actual reset happens at the end of the instruction

when nCS goes high.

4.1.2

SFR READ - READ

Figure 4-3 illustrates the READ instruction, while

accessing SFR. The instruction starts with nCS going

low. The Command (C<3:0> = 0b0011), is followed by

the Address (A<11:0>). Afterwards, the data byte from

address A (DB[A]) is shifted out, followed by data byte

from address A+1 (DB[A+1]). Any number of data

bytes can be read. The instruction ends when nCS

goes high.

4.1.3

SFR WRITE - WRITE

Figure 4-4 illustrates the WRITE instruction, while

accessing SFR. The instruction starts with nCS going

low. The Command (C<3:0> = 0b0010), is followed by

the Address (A<11:0>). Afterwards, the data byte is

shifted into address A (DB[A]), next into address A+1

(DB[A+1]). Any number of data bytes can be written.

The instruction ends when nCS goes high.

Data bytes are written to the register with the falling

edge on SCK following the 8th data bit.

FIGURE 4-2:

RESET INSTRUCTION

FIGURE 4-3:

SFR READ INSTRUCTION

FIGURE 4-4:

SFR WRITE INSTRUCTION

0b0000

0x000

nCS Low

nCS High

0b0011

A<11:0>

DB[A]

DB[A+1]

DB[A+n-1]

nCS Low

nCS High

0b0010

A<11:0>

DB[A]

DB[A+1]

DB[A+n-1]

nCS Low

nCS High

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