When the GPIB system operates in command mode (when ATN is asserted true), it can transmit the following types of commands:
Talk addresses
Listen addresses
Secondary addresses
Universal commands
Addressed commands
Unadress commands
Talk addresses can be in the range of 0 to 30, and consist of the value of the primary bus address added to the talk base address value of 64. In ATEasy, instruments can be configured to primary addresses of 0 to 30 (0 is typically used for the interface board).
Listen addresses can be in the range of 0 to 30, and consist of the value of the primary bus address added to the listen base address value of 32. In ATEasy, instruments can be configured to primary addresses of 1 to 30 (0 is reserved for the interface board).
Secondary addresses are used as components of listen or talk addresses. When secondary addresses are used, the listen or talk address consists of two bytes:
The first byte is the primary address.
The second byte is the secondary address. The secondary address can be in the range of 0 to 30. The secondary address is typically used in instruments that have many modules, or when accessing VXI instruments via a GPIB board.
Universal commands are received by all devices on the GPIB system. The following universal commands are available:
LLO (Local Lockout)—Disables local mode on the system. The front panel of the responding device cannot be operated.
DCL (Device Clear)—Returns all responding devices to an idle state.
PPU (Parallel Poll Unconfigure)—Disables parallel polling for all devices on the system that have parallel poll capabilities.
SPE (Serial Poll Enable)—Enables serial polling on the system.
SPD (Serial Poll Disable)—Disables serial polling on the system.
Addressed commands are recognized and executed only by active listeners. Using addressed commands, the controller can cause all active listeners on the system to perform a single command simultaneously.
The following addressed commands are available:
SDC (Selected Device Clear)—Returns the selected devices to an idle state.
GTL (Go To Local)—Returns selected devices to local mode, reinitializing front-panel operation of the system.
GET (Group Execute Trigger)—Causes selected devices to execute a pre- defined action.
PPC (Parallel Poll Configure)—Sets selected devices to respond to parallel polling. (See Polling for more information.)
TCT (Take Control)—Sets the selected device to be active controller.
UNL (Unlisten)—Sets all devices on the system to "not listen." (This command has no effect on devices that have a manual switch set to Listen Only.)
UNT (Untalk)—Sets any talker device on the system to "not talk."