Omega Products PCI-DIO24 Installation Manual

User's Guide

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e-mail: info@omega.com

PCI-DIO24 PCI-DIO24H PCI-DIO24H/CTR3

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. The formula for attenuation is:

Attenuation = R1+R2 R2

The variable

Attenuation

tional difference between the signal voltage max and the full scale of the

is the propor-

analog input.

For example, if the signal varies

2 = 10K+10K

10K

between 0 and 10 volts and you wish to measure that with an PCI-DIO24 board with a full scale range of 0 to 5 volts, the

Attenuation

is 2:1 or just 2.

For a given attenuation, pick a handy

R1=(A-1)*R2

resistor and call it R2, then use this formula to calculate R1.

Digital inputs can readily use voltage dividers. For example, if you wish to measure a digital signal that is at 0 volts when off and 24 volts when on, you cannot connect that directly to the PCI-DIO24 digital inputs. The voltage must be dropped to 5 volts max when on. The Attenuation is 24:5 or 4.8. Use the equation above to find an appropriate R1 if R2 is 1K. Remember that a TTL input is 'on' when the input voltage is greater than 2.5 volts.

IMPORTANT NOTE

The resistors, R1 and R2, are going to dissipate all the power in the divider circuit according to the equation Current = Voltage / Resistance. The higher the value of the resistance (R1 + R2) the less power dissipated by the divider circuit. Here is a simple rule:

For Attenuation of 5:1 or less, no resistor should be less than 10K.

For Attenuation of greater than 5:1, no resistor should be < 1K.

The CIO-TERMINAL is a 16" by 4" screw terminal board with two 37 pin D type connectors and 56 screw terminals (12 - 22 AWG). Designed for table top, wall or rack mounting, the board provides prototype, divider circuit, filter circuit and pull-up resistor positions which you may complete with the proper value components for your application.

7.2 TTL TO SOLID STATE RELAYS

TABLE OF CONTENTS

Many applications require digital outputs to switch AC and DC voltage motors on and off and to monitor AC and DC voltages. The se AC and high DC volt ages cannot be controlled or read directly by the TTL digital lines of a PCI-DIO24.

Solid State Relays

and monitoring of AC and high DC voltages and provide 750V isolation. Solid State Relays (SSRs) are the recommended method of interfacing to AC and high DC signals.

The most convenient way to use solid state relays and a PCI-DIO24 board is to purchase a Solid State Relay Rack. A SSR Rack is a circuit board with output buffer chips which are powerful enough to swit ch the SSR and sockets to plug SSRs into. SSR Racks are available from Computer Boards and most manufacturers of SSRs. If you have only a few outputs to cont rol, you may also wish to consider the DR-OAC or DR-ODC, single point, DIN mountable SSRs.

The high current outputs of the PCI-DIO24H and PCI-DIO24H/CTR3 boards are suitable to drive SSR’ directly but the CMOS outputs of the PCI-DIO24 do not have sufficient drive to connect directly to most SSRs. If you only want to drive one or two SSRs with CMOS outputs, all you need is a 74LS244 output buffer chip between the 82C55 output and the SSR. Of course the SSR will need 5 volt power as well.

, such as those available from Omega, allow control

7.3 VOLTAGE DIVIDERS

If you wish to measure a signal which varies over a range greater than the input range of a digital input, a voltage divider can drop the voltage of the input signal to the level the digital input can measure.

A voltage divider takes advantage of Ohm's law, which states,

1 INTRODUCTION

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2 QUICK START & INSTALLATION

2.1 WINDOWS 95, 98 & NT

2.2 DOS and/or Windows 3.1

2.3 InstaCal

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2.3 RUN InstaCAL

2.4 Testing The Installation

3 I/O CONNECTIONS

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3.1 CABLES AND SCREW TERMINAL BOARDS

3.2 CONNECTOR DIAGRAM - PCI-DIO24, -24H &

-24H/CTR3

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3.3 SIGNAL CONNECTION CONSIDERATIONS

3.4 COUNTER CONNECTIONS & SETUP

4 SOFTWARE

5 I/O REGISTER MAPS

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5.1 BOARD CONTROL REGISTERS

5.1 82C55 CONTROL & DATA REGISTERS

5.2 82C55 DIGITAL I/O REGISTERS

5.3 OUTPUT PORTS

5.4 INPUT PORTS

5.5 82C54 COUNTER CHIP

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2 2 3 3 3 4

5 5

5 6 7

8 10 11 12 13 14 15

Voltage = Current * Resistance

Implied in the above is that any variation in the voltage drop for the circuit as a whole will have a

portional

age drops in the circuit.

A voltage divider takes advantage of the fact that the voltage across

variation in all the volt-

pro-

Signal High

Signal

Vin

Volts

Signal Low

SIMPLE VOLTAGE DIVIDER - Vin = R1+R2

Vout R2

V2 Vout

CIO-DIO24 Input

Groundt

6 SPECIFICATIONS

6.1 PCI-DIO24

6.2 PCI-DIO24H

6.3 PCI-DIO24H/CTR3

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7 ELECTRONICS AND INTERFACING

7.1 PULL UP & PULL DOWN RESISTORS

7.2 TTL TO SOLID STATE RELAYS

7.3 VOLTAGE DIVIDERS

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16 16 17 18

20 20 22 22

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 i s in output mode, the 82C55 has mor e than enough power (2 .5mA) to over ride the pull-up/down resistor's high signal and drive the line to 0 volts. If the 82C55 asserts a high signal, the pull up resistor guaranties that the line goes to +5V.

Of course, a pull-down resistor accomplishes the same task except that the line is pulled low when the 82C55 is reset. The 82C55 has more than enough power to drive the line high.

The PCI-DIO24 series boar ds are equipped with positions for pull-up/down resistors Single Inline Packages (SIPs). The positions are marked A, B and C and are located beside the 82C55 or output chips.

A 2.2K, 8 resistor SIP is made of 8, 2.2K resistors all connected one side to a single common point and the other, each to a pin protruding from the SIP. The common line to which all resistor are connected also protrudes from the SIP. The common line is marked with a dot and is at one end of the SIP.

The SIP may be installed as pull-up or pull-down. At each location, A, B & C on the PCI-DIO24 series boards, there are 10 holes in a line. One end of the line is +5V, the other end is GND. They are so marked. The 8 holes in the middle are connected to the 8 lines of the port, A, B, or C.

A resistor value of 2.2K is recommended. Use other values only if you have calculated the necessity of doing so.

UNCONNECTED INPUTS FLOAT!

Keep in mind that unconnected inputs float. If you are using the DIO24 board for input, and have unconnected inputs, ignore the data from those lines.

In other words, if you connect bit A0 and not bit A1, do not be surp rised if A1 stays low, stays high or tracks A0... It is unconnected and so unspecified. The 82C55 is not malfunctioning. In the absence of a pull-up/down, any input to a PCI-DIO24 which is unconnected, is unspecified!

You do not have to tie input lines, and unconnected lines will not affect the performance of connected lines. Just make sure that you mask out any unconnected bits in software!

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. To prevent unwanted switching and to drive all outputs to a known state after power on or reset, pull all pins either high or low through a 2.2K resistor.

7.1 PULL UP & PULL DOWN RESISTORS

Whenever the 82C55 is powered on or reset, the control register is set to a known state. That state is mode 0, all ports input.

When used as an output device to control other TTL input devices, the 82C55 applies a voltage level of 0V for low and 2.5V-5V for high. It is the output voltage level of the 82C55 that the device being controlled responds to.

The concept of output voltage for an 82C55 in input mode is meaningless. Do not connect a volt meter to the floating input of an 82C55. It will show you nothing of meaning. In input mode the 82C55 is in 'high Z' or high impedance. If your 82C55 was connected to another input chip (the device you were controlling), the inputs of that chip are left floating whenever the 82C55 is in input mode.

1 INTRODUCTION

This manual provides information on PCI-DIO24, PCI-DIO24H and PCI-DIO24H/CTR3 digital I/O boards and accessories. The manual is organized into separate sections for those aspects of a product which are unique. Some issues, such as simple programming and electronic interfacing are applicable to all of the digital boards.

The PCI-DIO24 is a single 82C55 digital I/O chip interfaced to the PCI bus, with all its I/O lines accessible through the board's 37 pin connector. The I/O pins of an 82C55 are CMOS TTL level.

PCI-DIO24H is a high drive, 24 line digital I/O board. The control register which sets the direction of the I/O ports is identical to an 82C55 in mode 0 (see 82C55 data sheet). The I/O pins are high drive TTL capable of sourcing 15mA and sinking 64mA.

PCI-DIO24H/CTR3 is a PCI-DIO24H with an 82C54 counter added. The 82C54 is a 10MHz down-counter chip with three 16 bit counters. The functions of the counter (Input, Gate and Output) a re brought o ut to those pins which ar e used for b us power access on the PCI-DIO24 and PCI-DIO24H. The PCI-DIO24H/CTR3 uses 8 I/O addresses. The lower four are occupied by the 82C55 digital I/O chip emulation and the upper four are occupied by the 82C54 counter timer chip.

This manual provides information on programming the 82C55 in mode 0. Those wishing to use the 82C55 in modes 1 or 2, or who wish to program the 82C54 counter on the PCI-DIO24H/CTR3, must procure a data book from Intel Corporation Literature Department.

If the inputs of the device you are controlling are left to float, they may float up or down. Which way they float is dependent on the characteristics of the circuit and the electrical environment; and may be unpre dictable! This is why it often appears that the 82C55 has gone 'high' after power up. The result is that your controlled device gets turned on! That is why you need pull up/down resistors.

Shown here is one 82C55 digital output with a pull-up resistor attached.

All these products are supported by Universal Library programming library. As an owner of this product, you are entitled to the latest revision of the manual and software. Just call with your cur rent revision numbers ha ndy, and request an upd ate be sent to you.

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