TNT4882 Programming Considerations Chapter 4
Responding to Serial Polls
If STBO IE = 0 when the CIC serial polls the TNT4882, the TNT4882 sends the STB to the CIC without the host interface intervening.
If the contents of the STB are likely to change between the time you issue reqt and the time the CIC serial polls the TNT4882, you can use the STBO IE bit. When
STBO IE = 1, the TNT4882 does not respond to a serial poll immediately. Instead, when the CIC serial polls the TNT4882, the TNT4882 generates an interrupt. In response to this interrupt, the host interface writes the STB to the SPMR (write 0 to bit 6). The
TNT4882 responds to the serial poll by sending the STB to the CIC.
When the TNT4882 sends the STB to the CIC, the TNT4882 asserts the GPIB DIO7 signal if the TNT4882 is requesting service. The CIC normally reads the STB once, but if the CIC asserts ATN between each 1-byte read, it can read the STB any number of times. The TNT4882 asserts the GPIB DIO7 signal, however, only during the first read.
After the first read, rsv clears. PEND clears when the CIC asserts ATN to terminate the serial poll.
The TNT4882 asserts the GPIB EOI line during a serial poll if the SPEOI bit of AUXRB is set.
Responding to Parallel Polls
The ist Message
When it responds to a Parallel Poll, the TNT4882 can transmit only one bit of information to the CIC. This one bit contains the status of the ist message. If the Individual Status
Select (ISS) bit in AUXRB is one, ist is true if the TNT4882 is asserting the SRQ signal
—that is, the IEEE 488.1 Service Request function of the TNT4882 is in the SRQS state.
If ISS = 0, you set and clear the ist message by using the ist and ~ist auxiliary commands.
If ISS = 0, the meaning of the ist message is device dependent.
Remote Configuration
Before the CIC can poll the TNT4882, the TNT4882 must first be configured to respond to parallel polls. The host interface can locally configure the TNT4882 (IEEE 488.1
capability code PP1) or the TNT4882 can let the CIC remotely configure the TNT4882
(IEEE 488.1 capability code PP2).
To let the CIC remotely configure the TNT4882, clear the PP2 bit in AUXRI. Do not write to the PPR. The CIC configures the TNT4882 without software intervention, and it enables or disables the TNT4882 to respond to parallel polls. The CIC configures the polarity of the response of the TNT4882, and it also selects the GPIB data line that the
TNT4882 uses to respond to parallel polls.
TNT4882 Programmer Reference 4-14 © National Instruments Corp.
