@nyc_(is_out_of_here) wrote:
Can some explain to me what it is and most importantly how I need to deal with it?
A normal flow of communication on the GPIB is to send some command bytes (with the ATN line asserted) to place the devices on the bus in the correct addressing state (1 device is addressed as a talker and 1 or more devices are addressed as a listener). Afterwards, the ATN line is unasserted and the talker will place data bytes on the bus for the listeners to listen to.
With the NI-488.2 device-level API, the driver normally caches the current addressing state of the bus. If you do multiple consecutive commands and the addressing state is already in the correct state, NI-488.2 will skip the addressing portion. For example (using a pseudocode type of syntax):
ibwrt (dev2, "*cls", 4); -> Across the bus you will see ATN^, UNL, MTA0, MLA2, ATNv, *CLS
ibwrt (dev2, "*idn?", 5); -> Across the bus you will see *IDN?
ibrd (dev2, 100); -> Across the bus you will see ATN^, UNL, MTA2, MLA0, ATNv, [Response from Instrument]
As you can see, the second ibwrt did not have the addressing bytes because of the address caching. If you enable readdressing, NI-488.2 skips the address caching and always sends out the command bytes. With readdressing enabled, the same calls would look like:
ibwrt (dev2, "*cls", 4); -> Across the bus you will see ATN^, UNL, MTA0, MLA2, ATNv, *CLS
ibwrt (dev2, "*idn?", 5); -> Across the bus you will see ATN^, UNL, MTA0, MLA2, ATNv, *IDN?
ibrd (dev2, 100); -> Across the bus you will see ATN^, UNL, MTA2, MLA0, ATNv, [Response from Instrument]
I believe the previous reply indicated how to enable/disable readdressing, but I wanted to answer your "what is it" so that you can understand the implication on the bus.
