Si53112

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4. Control Registers

4.1. Byte Read/Write

Reading or writing a register in an SMBus slave device in byte mode always involves specifying the register

number.

4.1.1. Byte Read

The standard byte read is as shown in Figure 8. It is an extension of the byte write. The write start condition is

repeated; then, the slave device starts sending data, and the master acknowledges it until the last byte is sent. The

master terminates the transfer with a NAK, then a stop condition. For byte operation, the 2 x 7th bit of the

command byte must be set. For block operations, the 2 x 7th bit must be reset. If the bit is not set, the next byte

must be the byte transfer count.

Figure 8. Byte Read Protocol

4.1.2. Byte Write

Figure 9 illustrates a simple, typical byte write. For byte operation, the 2 x 7th bit of the command byte must be set.

For block operations, the 2 x 7th bit must be reset. If the bit is not set, the next byte must be the byte transfer count.

The count can be between 1 and 32. It is not allowed to be zero or to exceed 32.

Figure 9. Byte Write Protocol

Slave

T

Wr

A Command

Slave

A

Rd

Data Byte 0 N P

A r

Command

starT

Condition

Byte Read Protocol

Acknowledge

repeat starT

Not ack

stoP

Condition

Register # to

read

2 x 7 bit = 1

17

1 1

8

1 1

7

1

18

1 1

Master to

Slave to

Slave

T

Wr

A Command

Data Byte 0

A

Command

starT Condition

Byte Write Protocol

Acknowledge

Register # to

write

2 x 7 bit = 1

17

1 1

8

1

8

1

1

Master to

Slave to

A P

stoP Condition