MCP48FVB01 datasheet(53/84 Pages) MICROCHIP

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DS20005466A-page 53

MCP48FVBXX

7.0.3

ERROR CONDITION

The Command Error (CMDERR) bit indicates if the

five address bits received (AD4:AD0) and the two

command

bits

received

(C1:C0)

are

valid

combination (see Figure 7-1). The CMDERR bit is

high if the combination is valid and low if the

combination is invalid.

SPI commands that do not have a multiple of eight

clocks are ignored.

Once an error condition has occurred, any following

commands are ignored. All following SDO bits will be

low until the CMDERR condition is cleared by forcing

the CS pin to the inactive state (VIH).

7.0.3.1

Aborting a Transmission

All SPI transmissions must have the correct number of

SCK pulses to be executed. The command is not

executed until the complete number of clocks has

been received. If the CS pin is forced to the inactive

state (VIH), the serial interface is reset. Partial com-

mands are not executed.

SPI is more susceptible to noise than other bus

protocols. The most likely case is that noise corrupts

the value of the data being clocked into the

MCP48FVBXX or the SCK pin is injected with extra

clock pulses. This may cause data to be corrupted in

the device, or a Command Error to occur, since the

address and command bits were not a valid

combination. The extra SCK pulse will also cause the

SPI data (SDI) and clock (SCK) to be out of sync.

Forcing the CS pin to the inactive state (VIH) resets the

serial interface. The MCP48FVBXX’s SPI interface will

ignore activity on the SDI and SCK pins until the CS

pin transition to the active state is detected (VIH to VIL).

7.0.4

CONTINUOUS COMMANDS

The device supports the ability to execute commands

continuously. While the CS pin is in the active state

(VIL), any sequence of valid commands may be

received.

The following example is a valid sequence of events:

CS pin driven active (VIL)

Read

command

Write

command (Volatile memory)

CS pin driven inactive (VIH)

Note 1:

When data is not being received by the

MCP48FVBXX, it is recommended that the

CS pin be forced to the inactive level (VIH).

It is also recommended that long

continuous command strings be broken

down into single commands or shorter

continuous

command

strings.

This

reduces the probability of noise on the

SCK pin corrupting the desired SPI

commands.

Note 1:

It is recommended that while the CS pin is

active, only one type of command should

be issued. When changing commands, it

is advisable to take the CS pin inactive

then force it back to the active state.

It is also recommended that long

command strings should be broken down

into shorter command strings. This

reduces the probability of noise on the

SCK pin, corrupting the desired SPI

command string.

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