CHAPTER 5. PERIPHERAL HARDWARE FUNCTIONS

(iii)Command formats

The transfer format of each command is shown below.

READ command

This command performs a read from the slave. The read data length is variable between 1 and

256 bytes, and is specified as a parameter by the master. If 00H is specified as the data length, this is interpreted as a 256-byte data transfer specification.

Fig. 5-54 READ Command Transfer Format

M

READ

Command

S

ACK

M

Data Length

Data

S

ACK

S

Data 0

Data

S

ACK

S

Data N

Data

S

ACK

Remarks M : Output by master

S : Output by slave

After the slave receives the data length, if the transmissible data is equal to or greater than that data length, the slave returns ACK. If the data is insufficient, ACK is not returned and an error is generated.

When a data transfer is performed, the slave compares the SIO contents before and after the transfer to check whether the data was correctly output onto the bus. If the SIO contents before and after the transfer are different, ACK is not returned and an error is generated.

WRITE, END and STOP commands

This command performs a data write to the slave. The write data length is variable between 1 and

256 bytes, and is specified as a parameter by the master. If 00H is specified as the data length, this is interpreted as a 256-byte data transfer specification.

Fig. 5-55 WRITE & END Command Transfer Format

M

 

 

S

 

M

WRITE

 

 

ACK

 

 

Data Length

 

 

 

 

 

 

 

Command

 

 

 

 

 

Data

Remarks M : Output by master

S : Output by slave

S

ACK

M

Data 0

Data

S

ACK

M

Data N

Data

S

ACK

M

END

Command

S

ACK

121

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NEC PD75P402, PD75402A user manual Iii Command formats, ➀ Read command, ➁ WRITE, END and Stop commands, 121