Chapter 6
Theory of Operation
© National Instruments Corporation
6-3
GPIB-1014 User Manual
Control Equations of Transceivers
Table 6-1 lists the control equations for the address and data.
Table 6-1. Control Equations of Transceivers
VMEbus Signals
Transceivers
Control Equations
A23 through A16
AS573
OC* = OWN* (output enable)
C = UAS (input clock)
A15 through A8
AS573
OC* = OWN* (output enable)
C = UAS (input clock)
A7 through A1
F245
EN* = low (output enable)
DIR = OWN (transceiver's direction)
HIBYTE transceiver
F245
EN* = HIBYTE*
DIR = (BWR* & OWN*) + (BWR &
OWN)
AM lines, IACK*, LWORD*
F241
EN* = OWN*
D15 through A8
F245
EN* = (ACKEN* & DBEN*) +
NEW_CYCLE* + DIACK
DIR = (BWR* & OWN*) + (BWR &
OWN)
D7 through D0
F245
EN* = (((ACKEN* & DBEN*) +
NEW_CYCLE*) & (BRDEN* + DS*)) +
HIBYTE
DIR = (BWR* & OWN*) + (BWR &
OWN)
Address Decoding
During non-DMA operations, the GPIB-1014 acts as a VMEbus slave and monitors the lower 16
lines of the VMEbus address bus (A15 through A01), the Address Modifier Lines (AM5 through
AM0), and the VMEbus signals LWORD* and IACK*. Receivers and comparators are used to
recognize the GPIB-1014 base address during short I/O transfers.
Two 25LS2521 comparators recognize the short I/O base address of the GPIB-1014. Except for
Model 1S, the base address is selectable with jumpers located on the board or with strapped lines
routed to the P2 connector. The base address of the GPIB-1014 is recognized whenever the
VMEbus signal AS* is active (IACK* is inactive), the Address Modifier lines indicate a short
I/O operation, and VMEbus address lines A15 through A9 match the jumper selected base