Sending Remote Multiline Messages (Commands); Going From Active To Standby Controller - National Instruments Corporation GPIB-1014P User Manual

Section Five
Another Active Controller passes control to the GPIB-1014P by sending the TLC GPIB talk
address (MTA) followed by the GPIB Take Control (TCT) message. The TLC, upon receiving
these two messages (MTA and TCT), automatically becomes CIC when ATN is dropped. The
exact sequence of events is as follows:
1. The TLC receives the My Talk Address (MTA). The TLC then enters into Talker Addressed
State (TADS). This operation can be transparent to a program. The Talker Active (TA) bit in
the Address Status Register (ADSR) is set when the TLC receives its GPIB talk address.
2. The TLC receives the GPIB TCT message.
Note: Normally, a program does not have to read or respond to the TCT command message,
but it can read the TCT message in the Command Pass Through Register (CPTR) in
response to the assertion of the CPT status bit in Interrupt Status Register 1 (ISR1),
assuming that the CPT ENABLE bit of AUXRB has been previously set.
3. The current Active Controller sees the completed handshake, goes to idle, and unasserts ATN.
4. As soon as the ATN line on the GPIB is unasserted, the TLC automatically becomes CIC and
asserts ATN.
As soon as the TLC becomes CIC, the CIC bit in the ADSR, and the Command Output (CO) bit in
Interrupt Status Register 2 (ISR2) are set. Using these two bits, the program can unambiguously
determine that the TLC is the GPIB Active Controller and can send remote messages.

Sending Remote Multiline Messages (Commands)

The GPIB-1014P sends commands as Active Controller simply by writing to the Command/Data
Out Register (CDOR) in response to the CO status bit in ISR2.
The TLC recognizes any commands applicable to itself, such as its own talk or listen address. To
make the TLC a Listener, write its listen address to the CDOR.

Going from Active to Standby Controller

If the TLC is GPIB Active Controller, the Controller Standby State (CSBS) is entered upon
reception of the Go To Standby auxiliary command. The ATN line is unasserted as soon as the
TLC enters CSBS. Even though the TLC GPIB Controller state machine is in standby, the CIC bit
in the ADSR is still set. Do not issue the Go To Standby auxiliary command unless the CO bit in
ISR2 is set.
There are three cases to consider when going to standby:
Case 1: The TLC becomes the GPIB Talker when ATN is unasserted. To do this, wait for CO to
be set, send the TLC GPIB Talk Address (MTA), wait for CO to be set again, and then
issue the Go To Standby auxiliary command.
© National Instruments Corporation 5-3
Programming Considerations
GPIB-1014P User Manual