GPIB Addresses
All GPIB devices and boards must be assigned a unique GPIB address. A GPIB address is made up of two parts: a primary address and an optional secondary address.
Most devices just use primary addressing. The GPIB Controller manages the communication across the GPIB by using the addresses to designate which devices should be listening or talking at any given moment. Typically your computer is the GPIB Controller and it manages communication with your GPIB device by sending messages to it and receiving messages from it.
The primary address is a number in the range 0 to 30. The Controller uses this address to form a talk or listen address that is sent over the GPIB when communicating with a device.
A talk address is formed by setting bit 6, the TA (Talk Active) bit of the GPIB address. A listen address is formed by setting bit 5, the LA (Listen Active) bit of the GPIB address. For example, if a device is at address 1, the Controller sends hex 41 (address 1 with bit 6 set) to make the device a Talker. Because the Controller is usually at primary address 0, it sends hex 20 (address 0 with bit 5 set) to make itself a Listener. The following table shows the configuration of the GPIB address bits.
| Bit Position | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| Meaning | 0 | TA | LA | GPIB Primary Address (range 030) | ||||
With some devices, you can use secondary addressing. A secondary address is a number in the range hex 60 to hex 7E. When you use secondary addressing, the Controller sends the primary talk or listen address of the device followed by the secondary address of the device.
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