VXI SM8000 - Manual (Page 58)

VXI Technology, Inc.
58 SM8000 Series Programming
T YPICAL O PTICAL A TTENUATOR C ONTROL E XAMPLE
The optical attenuator modules are controlled via an I 2 C 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.