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Understanding Timing diagrams of digital systems

Timing diagrams are the main key in understanding digital systems. Timing diagrams explain digital circuitry functioning during time flow. Timing diagrams help to understand how digital circuits or sub circuits should work or fit in to larger circuit system. So learning how to read Timing diagrams may increase your work with digital systems and integrate them. Bellow is a list o most commonly used timing diagram fragments: Low level to supply voltage: Transition to low or high level: Bus signals – parallel signals transitioning from one level to other: High Impedance state: Bus signal with floating impedance: Conditional change of on signal depending on another signal transition: Transition on a signal causes state changes in a BUS: More than one transition causes changes in a BUS: Sequential transition – one signal transition causes another signal transition and second signal transition causes third signal transition. As you see timing diagrams together with digital circuit can completely describe the circuits working. To understand the timing diagrams, you should follow all symbols and transitions in timing diagrams. You can find plenty of symbols in timing diagrams. It depends actually on designer or circuit manufacturer. But once you understand the whole picture, you can…

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Control motor PWM schematic

In general there are two ways to control DC motor speed: by varying supply voltage and pulse width modulation (PWM). First control method is not convenient especially in digital systems. It requires analog circuitry and so on. Second motor speed control method is very convenient for digital systems, because all control is made using only digital signals. As you already know PWM (Pulse Width Modulation) is all about switching speed and pulse width (duty cycle). Duty cycle is ratio of signal time ON/T. T is period of signal. In above diagram you see two signals. First duty cycle is about t1/T=1/3 and another’s duty cycle would be about t2/T=2/3. And notice the period of signals are the same. If we apply these signals to switching transistor we would get control over effective voltage across motor: Vefective=(tON/T)*Vcc; Where tON-signal on time over one period T. In this way you can control motor speed using microcontrollers PWM output or if you need you may use simple control motor PWM schematic constructed using IC555 timer circuit: Without going too deep in to 555 timer’s performance analysis I can mention that duty cycle can be changed using potentiometer RV1. The period of signal won’t…

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Programming AVR fuse bits – oscillator settings

I guess many of you were confused when programming AVR fuse bits. I get many newbie questions like “I programmed Atmega8 but it doesn’t work”. Then my standard answer is: “Did you touch configuration bits?” and if yes, then I am almost 90% sure that he did it wrong. Most of them understands wrongly that programmed fuse bit in configuration should be left unchecked and opposite. Let’s take a look at widely used programming software – PonyProg. First thing you do before programming chip is set configuration bits (Atmega8 in picture): The first attention should be paid to clock sources. There are Four bits controlling Atmega8 clock sources: CKSEL0, CKSEL1, CKSEL2, CKSEL3.

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Small note on how to start LCD in 4 bit mode

When LCD is working in 4 bit mode, then data has to be sent by nibbles – portions of 4 bits. Just remember that first goes high nibble then follows lower one. Each nibble has to be strobed with control signal E separately. Following list is describing how to start LCD in 4 bit mode: Wait for 15 ms after power is switched on; Write 00000011 (0x03) to LCD; Wait for 5 ms; Write 00000011 (0x03) to LCD; Wait for 160 us; Write 00000011 (0x03) to LCD; Wait for 160 us; Write 00000010 to enable 4 bit mode (after this command start sending in nibbles); Set interface length; Turn off display (0x00 and 0x08 nibbles); Write 00000001 (0x00 and 0x01 in nibbles) to clear display; Set cursor move direction by setting cursor bits; Enable display; After initialization is complete you may write any character or command to it.

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Connect LCD to Atmega using 3 wires

After I implemented interfacing LCD to ATmega8 using 2 wires https://scienceprog.com/interfacing-lcd-to-atmega-using-two-wires/ I decided to make another one example but with 3 wires. Using 3 wires makes control much simpler as it is easier to control data flow to shift register. Here I used the same super cheap 74HC164 serial in parallel out register. LCD to shift register is connected in 8 bit mode. LCD strobe pin E is controlled with Atmega PC2 pin. Register is clocked with PC1 and data is transferred with PC0 pin. Notice, that I used same data line (PC0) to control LCD RS pin. RS pin is controlled in this way: after 8 bits are sent to shift register, then enable data line by setting ‘1’ (PC0) without clocking and after this LCD E pin is strobed. For more details take a look at my source code at the end of article. If there is any questions, don hesitate to ask. Source code:3 Wire LCD interface to ATMEGA

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RTC example on ARM7 LPC2148 using WinARM

Finally got my LPC2148 RTC working on my development board. arm7 base development board for lpc2148 I am quite new to ARM microcontrollers, so I managed to make few tests using them by driving some peripherals and writing some test routines. First code I tried was simple LED blink program first lpc2148 arm7 microcontroller test led blink This one is running microcontrollers real time clock (RTC) and generating interrupts every second. When Interrupt occurs microcontroller sends particular message to UART that I could see via Terminal program. The main program: /****************************************************************************** * * WinARM RTC application * * – UART0 send in Interrupt-Mode * – Sends message every seccond. * – RTC interupt every second ******************************************************************************/ #include “types.h” #include “LPC214x.h” #include “config.h” #include “armVIC.h” #include “uart.h” uint32_t time_toggle=0; static void rtc0(void) __attribute__ ((interrupt (“IRQ”))); static void lowInit(void) { // set PLL multiplier & divisor. // values computed from config.h PLLCFG = PLLCFG_MSEL | PLLCFG_PSEL; // enable PLL PLLCON = PLLCON_PLLE; PLLFEED = 0xAA; // Make it happen. These two updates PLLFEED = 0x55; // MUST occur in sequence. // setup the parallel port pin IO0CLR = PIO0_ZERO_BITS; // clear the ZEROs output IO0SET = PIO0_ONE_BITS; // set the ONEs output…

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Microcontroller eats too much of RAM

All you know that microcontrollers have limited amount RAM and EEPROM. For instance ATMega128 has 4-Kbytes of RAM, 4-Kbyte of EEPROM. This may seem quite enough for some applications, but more complicated routines require more of RAM. And there is no compiler that can do better optimization on usage of ram than programmer. The main aim of reaching this is reducing dependence on global data, stack and the heap. So if your application running in microcontroller eats too much of RAM then you should develop some strategy of using its RAM. Lets see… if you use constants as global values, why not to move them to EEPROM area? You can easily do this by compiler when you declare your variables by using const keyword: const uint8_t a=10; I compiled some code using this declaration and compiler (AVR-GCC) compiled .eep file which can be burned to microcontrollers EEPROM. In this way you can store your constants to your EEPROM memory. Another factor eating microcontroller RAM is stacks. Try to use us much stack as your program require and leave some reserved space just in case. There are many techniques that can help define requirement of stack memory. One of them is…

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