Atmega16 Basics
#####Atmega16
First of all the stimulation can be tried with proteus and atmel studio. Thereafter we need to write the program using SP3000 or by directly connecting the board via USB. After all the simple stuff like blinking the LED and with Timers you can go on to do Serial communication, I2C communication between two atmega’s. There is a very good description about timers on MaxEmbeddeed.com. In AVR, there are three types of timers – TIMER0, TIMER1 and TIMER2. Of these, TIMER1 is a 16-bit timer whereas others are 8-bit timers. On completing the stimulation you should try to connect two atmega’s.
Now, as per the following formula, with a clock frequency of 32 kHz and 8-bit counter, the maximum delay possible is of 8 ms. This is quite low (for us, but not for the MCU). Hence for a delay of 6 ms, we need a timer count of 191. This can easily be achieved with an 8-bit counter (MAX = 255).
Thus, what we need to do is quite simple. We need to keep a track of the counter value. As soon as it reaches 191, we toggle the LED value and reset the counter. For this, we need the help of the following registers. TCNT, TCCR, TIMSK, TIFR… refer to http://maxembedded.com/2011/06/24/avr-timers-timer0/
###I2C communication An Inter-IC bus is often used to communicate across circuit-board distances. Here's a primer on the protocol. At the low end of the spectrum of communication options for "inside the box" communication is I2C ("eye-squared-see"). The name I2C is shorthand for a standard Inter-IC (integrated circuit) bus.
The before mentioned reference design is a bus with a clock (SCL) and data (SDA) lines with 7-bit addressing. The bus has two roles for nodes: master and slave:
- Master node — node that generates the clock and initiates communication with slaves
- Slave node — node that receives the clock and responds when addressed by the master The bus is a multi-master bus which means any number of master nodes can be present. Additionally, master and slave roles may be changed between messages (after a STOP is sent). There are four potential modes of operation for a given bus device, although most devices only use a single role and its two modes:
- master transmit — master node is sending data to a slave
- master receive — master node is receiving data from a slave
- slave transmit — slave node is sending data to the master
- slave receive — slave node is receiving data from the master
The master is initially in master transmit mode by sending a start bit followed by the 7-bit address of the slave it wishes to communicate with, which is finally followed by a single bit representing whether it wishes to write(0) to or read(1) from the slave.
If the slave exists on the bus then it will respond with an ACK bit (active low for acknowledged) for that address. The master then continues in either transmit or receive mode (according to the read/write bit it sent), and the slave continues in its complementary mode (receive or transmit, respectively). The address and the data bytes are sent most significant bit first. The start bit is indicated by a high-to-low transition of SDA with SCL high; the stop bit is indicated by a low-to-high transition of SDA with SCL high. All other transitions of SDA take place with SCL low.
If the master wishes to write to the slave then it repeatedly sends a byte with the slave sending an ACK bit. (In this situation, the master is in master transmit mode and the slave is in slave receive mode.) If the master wishes to read from the slave then it repeatedly receives a byte from the slave, the master sending an ACK bit after every byte but the last one. (In this situation, the master is in master receive mode and the slave is in slave transmit mode.)
The master then either ends transmission with a stop bit, or it may send another START bit if it wishes to retain control of the bus for another transfer (a "combined message").
The pins should be carefully connected especially to the VCC and ground. The internal clock of the Atmega16 may be 1Mhz or 16 Mhz. One should first try a simple LED Blinking program to test that. Regarding that information one can use the external clock with 22pf capacitors. Similarly the ADC terminal of Port A can be used for ADC. PC0 and PC1 for SDA and SCL respectively. ###Serial Communication Communication between two entities is important for the information flow to take place. In general the information transport system can be parallel in which the complete byte of data is sent at a time, with each bit having a separate dedicated line or it can be serial where only one communication line is available which is shared by all the bits sequentially. The RS232 port is most generally used in this case. Refer to this page for the actual circuit and how to use the USART registers