VXI SM8000 user manual Typical Optical Attenuator Control Example, Write

VXI Technology, Inc.

TYPICAL OPTICAL ATTENUATOR CONTROL EXAMPLE

The optical attenuator modules are controlled via an I2C bus interface. The bus protocol requires the transmission of the following:

•a Module Address

•a Command Byte

•the number of bytes to send

•the number of bytes to receive

•the proper data byte(s) that are to be written to, or received from, the optical module (the command byte(s)).

The following sequence should be used to control the modules:

Write

1.Load the Address Register with the module’s address. The default address of the modules as shipped from the factory is 73 => 49h. (This step may be skipped, see Address Register description.)

2.Load the Command Register with the number of bytes to be received plus 1, the number of bytes to be sent, and the proper command.

3.Write/Read the appropriate Relay Register 02 through 08 depending on the module being controlled.

Read

1.Load the Address Register with the module’s address. The default address of the modules as shipped from the factory is 73 => 49h. (This step may be skipped, see Address Register description.)

2.Load the Command Register with the number of bytes to be received plus 1, the number of bytes to be sent, and the proper command (a query command).

3.Write/Read the appropriate Relay Register 02 through 08 depending on the module being queried (write a “0”, the data is ignored).

4.Read the appropriate Relay Register 0A through 0C depending on the number of bytes that are to be received from the module being queried. See Attenuator Command Set.

Note

These read back registers are common to all four of the possible attenuator modules that may be installed. A subsequent write to any of the Relay Registers 02 through 08 will corrupt these registers.

58 SM8000 Series Programming