MCP413X datasheet(42/88 Pages) MICROCHIP

42 / 88 page

MCP413X/415X/423X/425X

DS22060B-page 42

6.1

SDI, SDO, SCK, and CS Operation

The operation of the four SPI interface pins are

discussed in this section. These pins are:

• SDI (Serial Data In)

• SDO (Serial Data Out)

• SCK (Serial Clock)

•CS (Chip Select)

The serial interface works on either 8-bit or 16-bit

boundaries depending on the selected command. The

Chip Select (CS) pin frames the SPI commands.

6.1.1

SERIAL DATA IN (SDI)

The Serial Data In (SDI) signal is the data signal into

the device. The value on this pin is latched on the rising

edge of the SCK signal.

6.1.2

SERIAL DATA OUT (SDO)

The Serial Data Out (SDO) signal is the data signal out

of the device. The value on this pin is driven on the

falling edge of the SCK signal.

Once the CS pin is forced to the active level (VIL or

VIHH), the SDO pin will be driven. The state of the SDO

pin is determined by the serial bit’s position in the

command, the command selected, and if there is a

command error state (CMDERR).

6.1.3

SDI/SDO

For device packages that do not have enough pins for

both an SDI and SDO pin, the SDI and SDO

functionality is multiplexed onto a single I/O pin called

SDI/SDO.

The SDO will only be driven for the command error bit

(CMDERR) and during the data bits of a read command

(after the memory address and command has been

received).

6.1.3.1

SDI/SDO Operation

Figure 6-2 shows a block diagram of the SDI/SDO pin.

The SDI signal has an internal “smart” pull-up. The

value of this pull-up determines the frequency that data

can be read from the device. An external pull-up can be

added to the SDI/SDO pin to improve the rise time and

therefore improve the frequency that data can be read.

Data written on the SDI/SDO pin can be at the

maximum SPI frequency.

On the falling edge of the SCK pin during the C0 bit

(see Figure 7-1), the SDI/SDO pin will start outputting

the SDO value. The SDO signal overrides the control of

the smart pull-up, such that whenever the SDI/SDO pin

is outputting data, the smart pull-up is enabled.

The SDI/SDO pin will change from an input (SDI) to an

output (SDO) after the state machine has received the

Address and Command bits of the Command Byte. If

the command is a Read command, then the SDI/SDO

pin will remain an output for the remainder of the

command. For any other command, the SDI/SDO pin

returns to an input.

FIGURE 6-2:

Serial I/O Mux Block

Diagram.

Note:

MCP41X1 Devices Only .

Note:

To support the High voltage requirement of

the SDI function, the SDO function is an

open drain output.

Note:

Care must be take to ensure that a Drive

conflict does not exist between the Host

Controllers SDO pin (or software SDI/SDO

pin) and the MCP41x1 SDI/SDO pin (see

Figure 6-1).

SDI/SDO

SDI

SDO

Control

“smart” pull-up

Open

Drain

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