NCP81111

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10

I2C USER COMMANDS

These commands operate on a subset range of address space and are primarily for use by end users during application

configuration.

USER_REG_READ

This command can read one or more bytes from the working register set. The address (USER_ADDR) specified with this

command is a working set address from the user address range (refer to the USER column in the Register Map). Only registers

which have read access (shown as (R) or (RW) in the USER column) can be read with this command. If the command is

specified with an address that does not have read access the device will respond with NA (not−acknowledge).

However, if a block of registers are read which start from a valid address, then via the auto−incrementing address point to

an address that does not have read access, then for those invalid registers the return value will be 00h (zeros). The invalid

registers do not stop the command, and the device will respond with an A (acknowledge). This allows a single

USER_REG_READ command to read a contiguous block of data even if it spans addresses that are not valid. Note that this

command requires a repeated START sequence to change the data direction. Also, for the final byte received by the master it

must signal end of data to the device by responding with a NA (not−acknowledge). This allows the device to release the data

line so the master can send the STOP sequence. If a long sequence of data is read, which due to the auto−incrementing address

exceeds the allowable address range, then the device will return zero values (00h) for bytes beyond the address boundary.

For a single−byte read the sequence is as follows:

S

I2C_ADDR+W

A

USER_REG_READ

A

USER_ADDR

A

Sr

I2C_ADDR+R

A

D0

NA

P

This will read the data from the working register map as shown:

Working Registers

Data

Address

D0

USER_ADDR

For a multi−byte read command the sequence is as follows:

S

I2C_ADDR+W

A

USER_REG_READ

A

USER_ADDR

A

Sr

I2C_ADDR+R

A

D0

A

D1

A

D2

A

...

NA

P

This will read the data from the working registers as shown:

Working Registers

Data

Address

D0

USER_ADDR

D1

USER_ADDR+1

D2

USER_ADDR+2

...

...

USER_REG_WRITE

This command will write one or more bytes into the working register set. The address (USER_ADDR) specified with this

command is a working set address from the user address range (refer to the USER column in the Register Map). Only registers

which have write access (shown as (RW) in the USER column) can be written with this command. If the command is specified

with an address that does not have write access the device will respond with NA (not−acknowledge). However, if a block of

registers are written which start from a valid address, then via the auto−incrementing address point to an address that does not

have write access, then for those invalid registers the input data will be ignored. The invalid registers do not stop the command,

and the device will respond with an A (acknowledge). This allows a single USER_REG_WRITE command to write a

contiguous block of data even if it spans addresses that are not valid. If a long sequence of data is written which exceeds the

allowable address range then the command will automatically terminate when the end of the address range is reached.

Attempting to write past this point will result in NA (not−acknowledge) responses from the device.