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one of the resistors in a circuit is proportional to the voltage across the total resistance in the circuit. The trick to using a voltage divider is to choose two resistors with the proper proportions relative to the full scale of the digital input and the maximum signal voltage. The phenomena of dropping the voltage proportionally is often called attenuation.
TABLE OF CONTENTS 7.2 TTL TO SOLID STATE RELAYS Many applications require digital outputs to switch AC and DC voltage motors on and off and to monitor AC and DC voltages. These AC and high DC voltages cannot be controlled or read directly by the TTL digital lines of a PCI-DIO24. Solid State Relays, such as those available from Omega, allow control and monitoring of AC and high DC voltages and provide 750V isolation.
The pull-up resistor provides a reference to +5V while its value of 2200 ohms requires only 2.3 mA of drive current If the 82C55 is reset and enters high impedance input, the line is pulled high. At that point, both the 82C55 AND the device being controlled will sense a high signal. If the 82C55 is in output mode, the 82C55 has more than enough power (2.5mA) to over ride the pull-up/down resistor's high signal and drive the line to 0 volts.
7 ELECTRONICS AND INTERFACING This short, simple introduction to the electronics most often needed by digital I/O board users covers a few key concepts. IMPORTANT NOTE It cannot be stated often enough to those unfamiliar with the 82C55, WHENEVER THE 82C55 IS POWERED ON OR RESET, ALL PINS ARE SET TO HIGH IMPEDANCE INPUT. The implications of this fact is that if you have output devices such as solid state relays, they may be switched on whenever the computer is powered on or reset.
2 QUICK START & INSTALLATION The installation and operation of all three of the PCI-DIO24 series boards is very similar. Throughout this manual we use PCI-DIO24 as a generic designation for the PCI-DIO24, PCI-DIO24H, PCI-DIO24H/CTR3. When required due to the differences in the boards, the specific board name is used. The PCI-DIO24 boards are easy to use. This quick start procedure will help you quickly and easily setup, install and test your board.
6.3 PCI-DIO24H/CTR3 2.2 DOS and/or WINDOWS 3.1 Digital Input / Output Digital Type Output: Input: Configuration 8255 emulation, Mode 0 74S244 74LS373 2 banks of 8, 2 banks of 4, programmable by bank as input or output 24 I/O 2.4 volts min @ -15mA 0.5 volts max @ 64 mA 2.0 volts min, 7 volts absolute max 0.8 volts max, -0.
InstaCal selects and sets the I/O address from the range of available addresses. The address and other information is stored in the configuration file CB.CFG. This file is accessed by the Universal Library for programmers. Note also that the Universal Library is the I/O board interface for packaged applications such as Labtech Notebook and HP-VEE, therefore the InstaCal settings must be made in order for these and other applications to run. The board’s base address is also stored in the system software.
6 SPECIFICATIONS 3 I/O CONNECTIONS 3.1 CABLES AND SCREW TERMINAL BOARDS 6.1 PCI-DIO24 Digital Input / Output Digital Type (Digital I/O connector) Configuration 82C55 2 banks of 8, 2 banks of 4, programmable by bank as input or output 24 I/O 3.7 volts min @ -2.5mA 0.4 volts max @ 2.5mA 2.2 volts min, VCC + .3 volts absolute max 0.8 volts max, -0.
3.3 SIGNAL CONNECTION CONSIDERATIONS All the digital outputs and inputs on the PCI-DIO24 as well as the counter/timer signals of the PCI-DIO24H/CTR3 connector are CMOS TTL. The PCI-DIO24H signals are buffered (high output drive) TTL. TTL is an electronics industry term, short for Transistor Transistor Logic, which describes a standard for digital signals which are either at 0V or 5V.
5.4 INPUT PORTS 3.4 COUNTER CONNECTIONS & SETUP In 82C55 mode 0 configuration, ports configured for input read the state of the input lines at the moment the read is executed, transitions are not latched. For information on modes 1 (strobed I/O) and 2 (bi-directional strobed I/O), you will need to acquire an Intel or AMD data book and see the 82C55 data sheet.
4 SOFTWARE Due to the complex and somewhat unpredictable nature of WINDOWS 95 control of Plug-and-Play addresses, we highly recommend that users take advantage of our Universal Library package's easy to use programming interfaces. However, if you are an experienced programmer, and wish to read and write directly to the board, we have provided a detailed register map in the next chapter.
The registers and their function are summarized in the following table. A more detailed description of each register is included in subsequent sections. Within each register are 8 bits which may constitute a byte of data or 8 individual bit set/read functions. ADDRESS BASE +0 BASE +1 BASE +2 BASE +3 READ FUNCTION Port A Input of 82C55 Port B Input Port C input None. No read back on 82C55.
5.1.2 USER I/O STATUS/CONTROL (PCI-DIO24H/CTR3 only) 5.1 BOARD CONTROL REGISTERS BADR1 + 50 (hex) 5.1.1 INTERRUPT STATUS/CONTROL READ/WRITE 31:8 7 BADR1 + 4C (hex) x READ/WRITE 31:8 7 x x 6 5 4 3 2 1 0 PCIINT x x x INT INTPOL INTE This register is 32-bits in length. Please note that the remainder of the register's bits have specific control functions.
