Logic Circuits

Many digitally controlled potentiometers (for example, the LM1971/2/3 from National Semiconductor, www.national.com) incorporate a three-wire serial digital interface, using data, clock, and enable lines. In Figure 1, the potentiometer's nomenclature for these lines is Data-In, Clk, and Load/Shift, respectively. The assembler program in Listing 1 provides an interface to an SAB80535 µC.

A project required building a synchronous-demodulator circuit to track a line drawn on paper. The beauty of the synchronous -modulator/ demodulator approach is its inherent noise rejection. The method rejects nearly all out-of-band noise, whether from internal drift or external illumination. This rejection is a boon in optical tracking, where the return signal is inevitably buried in 120-Hz ambient light, amplifier offsets, and temperature drifts.

Normally in this series of web pages, we connect something to the PC, to demonstrate the protocols at work. However this poses a problem with the keyboard. What could be possibly want to send to the computer via the keyboard interface? Straight away any devious minds would be going, why not a little box, which generates passwords!. It could keep sending characters to the computer until it finds the right sequence. Well I'm not going to encourage what could possibly be illegal practices.

It may be easy to find a precision voltage reference for your application; however, a programmable precision reference is another matter. The circuit in Figure 1 yields a precision reference with an LSB of 62.5 µV. The circuit is a 16-bit DAC using three 8-bit digital potentiometers and three CMOS op amps. Each digital potentiometer operates as an 8-bit multiplying DAC. On the left side of Figure 1, two digital potentiometers, IC3A and IC3B, span across VREF to ground, and the wiper outputs are connected to the noninverting inputs of two amplifiers, IC4A and IC4B.

You often need to convert a logic signal from one power-supply voltage to another. This conversion is a relatively simple task, unless the signal happens to be bidirectional. Serial buses such as Access.Bus, I2C, and SBI use bidirectional data lines. Some buses may require translating logic from one voltage to another; for example, from 3 to 5V. Figure 1 shows a simple solution to the conversion problem. The input signal can come from either side. In fact, you can drive both inputs low simultaneously (as in the I2C bus) without incurring latchup.

Alphanumeric LCD displays have become very popular for microcontroller applications because they can add a lot to a project in a variety of different ways. A text message giving the user instructions as well as feedback can make the application seem much more "professional" and easy to use. I like to use LCD's to help debug applications, with breakpoints set to display variable and I/O conditions and they are a lot cheaper than using a microcontroller emulator. To top it off, surplus LCD's can be found for a dollar or less.

A battery-powered, pushbutton-triggered TTL/CMOS-compatible source of debounced 5V logic pulses is a simple but handy piece of test equipment to have in any tool kit (Figure 1). The circuit's battery-powered operation complicates what would otherwise be a trivial exercise in switch-bounce and timing-circuit design. The convenient use of battery power simultaneously imposes two requirements: near-zero quiescent-current draw and input-variation-tolerant voltage regulation.

No Description available.

Using the circuit in Fig 1, a 68HC11 µP's stop instruction can put the µP's external RC-oscillator clock, as well as the µP itself, into a low-power mode. On receiving an interrupt, the µP will exit the stop condition and enable the RC clock. The RC clock, being a low-Q circuit, will start up immediately. Crystal oscillators, on the other hand, can waste precious milliseconds coming up to speed and stabilizing.

Figure 2 shows a block diagram for this sine-wave generator. You can easily analyze the generator's behavior by writing state equations in the z domain. You can also write equations in the s domain. The location of the two poles on the right-hand side reveals the generator's oscillatory nature. The inverse Laplace transformation is simple and results in a sine-wave statement.

The circuit in Figure 1 uses a Microchip 8-pin µC (PIC12C671) as a voltage-controlled oscillator (VCO). Because the PIC12C671 has an internal 4-MHz oscillator, four-channel 8-bit A/D converters, and built-in power-reset circuitry, you need no external components to configure the VCO. The µC reads two analog inputs through AN0 and AN1. The reference voltage for the A/D conversion is the µC's power supply VDD. The converted 8-bit data determines the duration of output high and output low. Assume, for example, the digitized outputs from AN0 and AN1 are 43 and 87, respectively. Timer 0 loads the 43 after the µC sets output GP2 to logic one. Timer 0 receives its timing from the internal clock.

As an integral part of an advanced computer science course in microcomputer systems it was thought that students could benefit from the design of a single board computer system based on a readily available microprocessor. This led to the project that is described in this paper. Most of the actual design work was done by James Antonakos as part of an Independent Study project. The result was a single board microcomputer system (SBMCS) that requires only a power supply and a serial monitor to be fully functional.

Pressing a single key on the keypad - will energize the relay. Entering a four-digit code of your choice - will de-energize it. The circuit was designed to control the Modular Burglar Alarm System - but it will have other applications. If you require added security - A Five-Digit Version - of the circuit is also available.

This application note demonstrates a simple bootloader implementation for the PIC18F families of microcontrollers with a CAN module. The goals of this implementation are to stress maximum performance and functionality, while requiring a minimum of code space. For users developing CAN enabled systems, it provides a low level framework that can be used with higher level network protocols to develop more complex and custom-tailored systems.

The purpose of this application note is to design a clock while multiplexing the features as much as possible, allowing the circuit to use the 18-pin PIC16C54. Other devices in the Microchip line expand on this part, making it a good starting point for learning the basics. This design is useful because it utilizes every pin for output and switches some of them to inputs briefly to read the keys. For a more extensive clock design, consult application note AN529.

The PIC16C5X/XX microcontrollers from Microchip Technology Inc., provide significant execution speed and code-compaction improvement over any other 8-bit microcontroller in its price range. The superior performance of the PIC16C5X/XX microcontrollers can be attributed primarily to its RISC architecture. The PIC16C5X/XX devices employ a Harvard architecture (i.e., has separate program mem-ory space and data memory space [8-bit wide data]). It also uses a two stage pipelining instruction fetch and execution.

Among the many features built into Microchip's Enhanced FLASH Microcontroller devices is the capability of the program memory to self-program. This very useful feature has been deliberately included to give the user the ability to perform bootloading operations. Devices like the PIC18F452 are designed with a designated 'boot block', a small section of protectable program memory allocated specifically for bootload firmware.

This application note describes the construction of a low cost serial programmer which uses a PC with a parallel (Centronix printer) port to control a PIC16C84. This programmer has the capability of programming a PIC16C84 microcontroller, and reading back internal data without removing the device from the target circuit. This feature is very useful in applications where changes in program code or program constants are necessary to compensate for other system features. For example, an embedded control system may have to compensate for variances in a mechanical actuator?s performance or loading.

Ever dream of having a Real-Time Kernel for the PIC16CXXX family of microcontrollers? Or ever wonder what Multitasking or Threads are all about? Then this article is for you. We will explore how to implement all of the features of a large Real-Time Multitasking Kernel in much less space, with more control, and with-out the large overhead of existing kernels. By planning ahead, and using the techniques outlined here, you can build your own fast, light, powerful, flexible real-time kernel with just the features needed to get the job done.

Since last December I have greatly inproved my robot. It no longer uses Infra Red technology to find its way, but instead it uses light to "see". The two photoresistors are used as eyeballs, the left one is used to turn left,the right is to turn right. The "feather sensor" has finally been worked out and will be used for turning the robot with out getting stuck on a corner. In other words when AI-A-1 turns left and is about to hit something the "feather sensor" touches the object and activats the reverse function. The robot has a circut with a capacitor and a power MOSFET that controlls how long to go in reverse. this circuit is coneceted to the "feather sensor" switch.