icl232 datasheet
Hello, Hello World You can get all the parts for this lecture . The first computers had serial ports that used RS232, and even current computers have serial ports or at least USB ports that act like RS232 ports . Both the computer and the device agreed on a speed of information - 'bits per second'. A computer would pass image data to a printer at 9600 bits per second and the printer would listen for this stream of 1s and 0s expecting a new bit every 1/9600 104us 104 micro-seconds, 0.000104 seconds . They have made an IC that is generically known as the MAX232 very close to RS232, no? The MAX232 is an IC originally designed by a company called Maxim IC that converts the /-12V signals of RS232 down to the 0/5V signals that our ATmega168 can understand. It also boosts the voltage of our ATmega168 to the needed /-12V of the RS232 protocol so that a computer can understand our ATmega168 and vice versa. To get our ATmega168 IC sending serial characters to a computer, we have to send these serial signals through a MAX232 circuit so that the computer receives /-12V RS232 signals. Don't worry if you're working with a chip labeled 'ICL232' or 'ST232' - these are just generics of the MAX232. MAX232 Circuit - Eagle / This MAX232 IC uses three 0.1uF capacitors C5, C6, C7 to operate go read about ' ' . As the MAX232 IC switches various signals from +/-12V to 0/5V it uses bits of current. A decoupling cap is meant to provide a quick burst of energy if the power supply dips down - sort of like a UPS system for your IC. The further the decoupling cap is from the IC, the less ability it has to provide that quick burst long wires have intrinsic capacitance of their own . The ATmega168 is going to send 5V signals to the MAX232 IC. The MAX232 IC in turn will convert those 5V signals to /-12V RS232 signals that the computer can understand through the DB9 port on the back of the computer. Let's just get through the Hyperterminal screens: More than likely, the serial port on your computer is COM1 The main settings are 9600bps and 8-N-1 . This means that the micro and the computer agree to talk at a rate of 9600bits per second bps and that each byte will have 8 data bits, with no parity bit, and only 1 stop bit. Pretty self explanatory, but just follow along: When you press the 'A' key on the computer in the hyperterminal window, a series of 1s and 0s get generated and pumped out the serial port on the back of your computer 8 bits: '01000001' to be specific 65d 41h - see for more info . These 0s and 1s hit the MAX232 on your breadboard which dutifully changes these RS232 signals to TTL signals. Because you've tied the TX and RX pins together R1OUT should be shorted to T1IN these 0s and 1s get sent right back out the MAX232 and down the DB9 serial cable. Now connect the TX and RX pins of the ATmega168 to the MAX232 circuit. Savvy travelers will note upside down the picture MAX232 IC is actually a SP3232 EBCP . Because circuits started to run on lower voltages 3.3V for instance the IC manufacturers had to redesign the MAX232 ICs to be more efficient so that they could take this lower voltage and boost it up to 12V for RS232. We are operating our breadboard at 5V but we are able to run our MAX232 from 3V up to 5V without problems.
icl232 datasheet
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