Chapter 5 Programming Considerations
© National Instruments Corporation 5-3 GPIB-1014 User Manual
9. Load the Parallel Poll response in the Parallel Poll Register (PPR) if local configuration is
used. If using remote configuration, clear the PPR.
10. Clear power on (pon) by issuing the Immediate Execute pon auxiliary command to the TLC
to bring the TLC online.
11. Execute the desired TLC auxiliary commands.
The registers associated with the 68450 DMAC do not need to be configured further until just
prior to a DMA operation.
The GPIB-1014 as GPIB Controller
The GPIB-1014 Controller function is generally in one of two modes: idle or in charge. When
in charge, the Controller function is either active (asserting ATN) or standby (not asserting
ATN). The following section discusses the various transitions between these two modes.

Becoming Controller-In-Charge (CIC) and Active Controller

The TLC can become CIC either by being the System Controller and taking control (by issuing
the Set IFC auxiliary command) or by being passed control of the GPIB from the current Active
Controller.
The GPIB-1014 is only capable of driving the GPIB IFC and REN lines (which allows the TLC
to function as GPIB System Controller) when the SC bit in CFG2 is set. To take control, issue
the Set IFC auxiliary command, wait for a minimum of 100 µsec, and then issue the Clear IFC
auxiliary command. The ensuing GPIB IFC message initializes the GPIB interface functions of
all devices on the bus. As soon as any existing CIC goes to idle (dropping ATN if it was active)
the TLC becomes CIC and Active Controller and asserts the GPIB ATN line.
Another Active Controller passes control to the GPIB-1014 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.
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 clearly
determine that the TLC is the GPIB Active Controller and can send remote messages.