Chapter 3 Hardware OverviewPCI-6023E/6024E/6025E User Manual3-6 ©National Instruments CorporationDigital I/OThe PCI-6023E, PCI-6024, and PCI-6025E boards contain eight lines ofdigital I/O (DIO<0..7>) for general-purpose use. You can individuallysoftware-configure each line for either input or output. At system startupand reset, the digital I/O ports are all high impedance.The hardware up/down control for general-purpose counters 0 and 1 areconnected onboard to DIO6 and DIO7, respectively. Thus, you can useDIO6 and DIO7 to control the general-purpose counters. The up/downcontrol signals are input only and do not affect the operation of the DIOlines.♦ PCI-6025E only:The PCI-6025E board uses an 82C55A Programmable Peripheral Interfaceto provide an additional 24 lines of digital I/O that represent three 8-bitports: PA, PB, PC. Each port can be programmed as an input or output port.The 82C55A has three modes of operation: simple I/O (mode 0), strobedI/O (mode 1), and bidirectional I/O (mode 2). In modes 1 and 2, the threeports are divided into two groups: group A and group B. Each group haseight data bits, plus control and status bits from Port C (PC). Modes 1 and2 use handshaking signals from the computer to synchronize data transfers.Refer to Chapter 4, Signal Connections, for more detailed information.Timing Signal RoutingThe DAQ-STC chip provides a flexible interface for connecting timingsignals to other boards or external circuitry. Your board uses the RTSI busto interconnect timing signals between boards, and the ProgrammableFunction Input (PFI) pins on the I/O connector to connect the board toexternal circuitry. These connections are designed to enable the board toboth control and be controlled by other boards and circuits.There are a total of 13 timing signals internal to the DAQ-STC that can becontrolled by an external source. These timing signals can also becontrolled by signals generated internally to the DAQ-STC, and theseselections are fully software-configurable. Figure 3-3 shows an example ofthe signal routing multiplexer controlling the CONVERT* signal.
