Chapter 3 Signal ConnectionsDAQCard-1200 User Manual 3-18 © National Instruments CorporationTiming SpecificationsUse the handshaking lines STB* and IBF to synchronize input transfers.Use the handshaking lines OBF* and ACK* to synchronize outputtransfers.The following signals are used in the timing diagrams shown later in thischapter:Name Type DescriptionSTB* Input Strobe Input—A low signal on this handshaking line loads data into theinput latch.IBF Output Input Buffer Full—A high signal on this handshaking line indicates thatdata has been loaded into the input latch. This is primarily an inputacknowledge signal.ACK* Input Acknowledge Input—A low signal on this handshaking line indicatesthat the data written from the specified port has been accepted. Thissignal is primarily a response from the external device that it hasreceived the data from the DAQCard-1200.OBF* Output Output Buffer Full—A low signal on this handshaking line indicatesthat data has been written from the specified port.INTR Output Interrupt Request—This signal becomes high when the 82C55Arequests service during a data transfer. Set the appropriate interruptenable signals to generate this signal.RD* Internal Read—This signal is the read signal generated from the parallel portinterface circuitry.WRT* Internal Write—This signal is the write signal generated from the parallel portinterface circuitry.DATA Bidirectional Data Lines at the Specified Port—This signal indicates when the dataon the data lines at a specified port is or should be available.
