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1. INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR DRIVERS
2. INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR SOFTWARE
3. INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR CODE
4. INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR FREE

After acquiring the data from an input port, additional software commands can use the information to make decisions. Software examples in this chapter illustrate byte transfers, and they assume, unless shown otherwise, that a programmer has defined variables, such as input_port_number, portdata, and abcxyz to hold values. The following command would obtain data from the port shown earlier in Figure 3-1: The general command above addresses a specific port (input_port_number) and assigns the data from the port to a variable, in this case, portdata. This command causes the computer to generate the needed strobe pulse at the input port so that the port data flows onto the bus: Transfer of data from an external device through an input port to a computer requires a software command. These devices provide the capability to disconnect outputs from a bus or other conductor that carries signals from several sources.

INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR DRIVERS

You may hear designers refer to similar devices called three-state bus drivers or three-state buffers. In this state, they appear electrically disconnected from the data bus. These gates provide the normal logic-1 and logic-0 outputs, and they also provide a disconnected or third state. The disconnect operation requires special gates with three-state outputs. At all other times, they must “disconnect” from the bus. To avoid conflicts on the CPU bus, input ports must “connect” themselves to the CPU data bus only when they receive the proper strobe pulse. Times, the port “disconnects” from the bus using three-state logic. As always, the external signals, the input-port circuits, and the computer must share a common ground.Ī simple 8-bit input port places information on the bus only when the computer places a short logic-0 pulse on the IN303* line. The input port shown in Figure 3-1 might accept signals from on-off switches or other devices that produce TTL-compatible signals. Some computers reserve I/O port numbers for internal and future use.) You can use port numbers within the ranges specified for the computer and software you plan to use. (Our port-number assignments carry no significance and simply serve as examples. We’ve used them to form a complete 8-bit input port. The single 74LS244 IC used in the example contains two independent 4-bit circuits. Any information present at the port’s eight inputs gets transferred to the CPU when the strobe pulse, IN303*, arrives. Only one device can use the bus at a time.įigure 3-1 shows a typical input port. To control the transfer of data from an input port to the computer, the computer requires a port-control command that identifies a specific port. That pulse “tells” a port when to transfer data onto the data bus so the CPU canĬapture it. The central processing unit (CPU), or its control circuits, provide a unique strobe pulse for each input port. The computer simply retrieves the specified data as requested by a software command.Īt its simplest, an input port acts like a “gate” that lets information pass from an external device to a computer’s data bus at a specific time.

Similarly, an input port connected to a digital thermometer would let a computer read temperature values at any time. An electronic counter in the controller would provide data that a computer could obtain from an input port. Imagine a controller that counts parts on a conveyor belt. You can think of many practical uses for input ports. Computers also receive data from keyboards, disk drives, touchscreens, and similar devices, all of which transfer their information to a computer through a device called an input port. Chapter 3 – Digital Inputsįew computers can operate without connections to external devices such as sensors, switches, or other equipment that informs software about external conditions.

INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR FREE

The Digital I/O Handbook is FREE with any qualifying Sealevel Digital I/O product purchase. You can purchase the Digital I/O Handbook for $19.95 by clicking here. It’s the sort of quick-start of real value to people with no experience in the field.” – Jack Ganssle, The Embedded Muse, January, 2005. This is a great introduction to the tough subject of tying a computer to the real world.

INPUT TO OUTPUT VOLTAGE RELATIONSHIP IN OPTICAL ISOLATOR CODE

Most pages have a bit of code plus a schematic. “What I like most is its mix of hardware and software. Detailed glossary of common industry terms.Shows many helpful circuit diagrams and drawings.Covers a wide range of devices including optically isolated inputs, relays, and sensors.Whether you are a practicing engineer or a student, The Digital I/O Handbook will provide helpful insight you will use again and again. Renowned technical author Jon Titus and the President and CEO of Sealevel Systems, Tom O’Hanlan, clearly explain real-world digital input/output implementation from both a hardware and software perspective. A Practical Guide to Industrial Input & Output Applications