Pic Serial Communication Assembly Code: A Guide to Configuring the SPBRG and TXSTA Registers

SidebarI/O Port usage summaryPORT register: TRISIO - The port directionregister.You can reset bits (low) to define port pins asoutputs.You can set bits (high) to define port pins asinputs.PORT register : GPIO -The input/output register.You write to this register to set outputpins high or low.You read from this register to read thecurrent value input pins.All of these actions were used in theprevious two tutorial pages and the all work using bit values:TRISIO = 0x01; sets bit 0 of TRISIO all the rest zero.TRISIO = 0x04; sets bit 2 of TRISIO all the rest zero.GPIO = 0x01; sets bit 0 of GPIO all the rest zero.GPIO = 0x04; sets bit 2 of GPIO all the rest zero.Note: In otherPIC devices ports are labeled alphabetically and they do not use the GPIO nameinstead they use the text 'PORT'. So the first port is labeled PORTA the nextPORTB etc. Corresponding port direction registers are TRISA and TRISB. Youcan use them in exactly the same way as GPIO andTRISIO.PIC Serial Port : Software TXpartThe code for theTX part of the USART is simplified in that it generates 10 bits of serial datawith no parity bit.The basic PIC Serial port configuration for the TX software is:if(typeof ez_ad_units!='undefined')ez_ad_units.push([[580,400],'best_microcontroller_projects_com-medrectangle-3','ezslot_4',107,'0','0']);__ez_fad_position('div-gpt-ad-best_microcontroller_projects_com-medrectangle-3-0');Bits per second (BAUD)2400Number of bits8ParityNoneStop bits1Flow controlNoneNote: To review how the RS232 pic serial portworks click here.Since each bit takes 1/2400 seconds the total time to transmit a digit is4.16ms.Note: The bit timing won't be exact as thePIC chip runs at 4MHz but it will be good enough for bench top use.CircuitThe circuit uses the standard MAX232 level translator chip but you could usean SP202ECP which has identical pin out (and is cheaper!) and lets you use100nF capacitors instead of electrolytic ones. You can also use USB to RS232 or USB to SerialDigital converters and with these you don't even need the MAX232 levelconverter everything is done at 5V (or 3V3)..Connect the ground and transmit output to a serial port connector as shown andto a serial cable from it to the PC and it's ready to go.For setting up Tera Term click here.SolderlessbreadboardAdd the MAX232 Chip and capacitors.Learn about the tool used for creatingthis diagram.Circuit diagramAgain the picserial port circuit is easier to see on a schematic.12F675 pinoutsOther views:SoftwareSource code files :To get the filesoftware project files and c source code click here.PIC Serial Port OperationThe code flashes the LED 3 times then repeats a message to the serialport.The following code is part of the pic serial port transmitter://////////////////////////////////////////////////////////////////////void_Soft_USART_Write(unsigned short chr) {unsigned short mask=1,i;unsigned int txdata; txdata = chr ProgramMemory.Scroll to bottom and check the CAL value at the last location.Now go back to the project Options and turn off "Program calibrationmemory" which will now be protected (until you lose it again!).Re Check it has workedYou can check it worked by re-building the original hex file (so themanually inserted CAL value is lost). Re-program this new hex into the PIC.Then upload the hex data. View memory as above and scroll to bottom - the newCAL value will be there.OSCCAL settingsThis register changes the oscillation frequency when you write to itMaximumfrequency0xFFMiddlefrequency0x80Minimumfrequency0x00Only the upper six bits are used as the calibration bits so values must bedifferent by 4 to change to the next OSCCAL setting e.g. values 32,33,34 and 35would give the same frequency setting.Microchip calibrates the 12F675 microcontroller and places a calibration valueat address 0x3FF. This is a RETLW instruction that returns a value when CALLedthis is the value to use in the OSCCAL register.ImportantYou have to write and use a routine to set the register OSCAL with thestored value : It is not done automatically for you!Note: You have to use the followingassembler code:The code the data sheet suggests you use to set the calibration value into theOSCCAL register is :bsf STATUS, RP0; Bank 1call 0x3ff; Get the cal valuemovwf OSCCAL; Calibratebcf STATUS, RP0; Bank 0All this does iscall the location that contains the RETLW value which then returns thecalibration value. This assembler code is packaged intothe get_set_osc_cal() routine and does the OSCCAL setting for you.Note:If the value stored at location 0x3ff is zero the oscillator may not work so-don't call this function if the CAL value is corrupted.Recovering lost calibrationIf you loose the calibration value then you'll need to re-calibrate -the best way is to set the internal clock at an output pin (Fosc/4) using thechip settings so you will be looking for 1MHz at the clock out pin.Use a frequency counter to measure the output (you can find a project on thissite here). Change the OSCCAL value untilyou find the one closest to 1MHz.To get the value back into the 12F675 use ICPROG and put the hex code RETLWinstruction at address 0x3FF. The first byte of the instruction is 0x34 andthe second is the value returned so for a calibration value of 0x20 you wouldput: 0x3420 at address 0x3FFRe-program the chip.Note: See the tip for storing thecalibration value so you will never forget it or loose it again.Back12F675 Tutorial IndexNext

PIC microcontrollers, obviously, can do more than just light up LEDs or reading button states. Microcontrollers can also communicate with another microcontroller or with other devices like sensors, memory cards, etc. Often the communication is done serially, where data bits are sent one at a time.

Pic Serial Communication Assembly Code

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The microcontroller serial communication article provides more information about this communication method. In this article, we will look at how to implement serial communication with PICs both in assembly language and in XC8.

The first part of the code above configures the serial port by making SPBRG = 25 (as per the calculations on our example calculation) and enabling transmit (at high speed, async) and receive ports via TXTSA and RCSTA.

Well, now you should know how shift registers are actually working. Frankly speaking, serial communication is as simple as connecting a couple of shift registers together! Connecting the data output of a shift register to be the data input of the other shift register enables us of sending digital data serially from an end to another!

As you might have noticed, it takes only 1-clock to transfer the data from a transmitter device to the receiver! Frankly speaking, we can theoretically transfer any number of bits (or bytes) using parallel communication protocols in a single clock cycle at a time. Here is a brief comparison between serial communication and parallel communication protocols.

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PIN DIAGRAM \uf0d8W\uf0d8W hen two processors are to communicate, more often the communication is organized in a bit serial fashion The.\n \n \n \n \n "," \n \n \n \n \n \n PIC Microcontroller and Embedded Systems 1\/e By Muhammad Mazidi, Rolin McKinlay, and Danny Causey \u00a9 2008 Pearson Education, Inc. Pearson Prentice Hall.\n \n \n \n \n "," \n \n \n \n \n \n Programming PIC 16F84A in Assembly. PIC16F84 pin-out and required external components.\n \n \n \n \n "," \n \n \n \n \n \n 8251 USART.\n \n \n \n \n "," \n \n \n \n \n \n Criteria for choosing a microcontroller A microcontroller must meet the task at hand efficiency and cost effectively. Speed. What is highest speed of.\n \n \n \n \n "," \n \n \n \n \n \n TIMERS.\n \n \n \n \n "," \n \n \n \n \n \n Chapter 9 PIC18 Timer Programming in Assembly\n \n \n \n \n "," \n \n \n \n \n \n The HCS12 SCI Subsystem A HCS12 device may have one or two serial communication interface. These two SCI interfaces are referred to as SCI0 and SCI1. The.\n \n \n \n \n "," \n \n \n \n \n \n Serial mode of data transfer\n \n \n \n \n "," \n \n \n \n \n \n RS-232 Communications.\n \n \n \n \n "," \n \n \n \n \n \n INT. TO EMBEDDED SYSTEMS DEVELOPMENT\n \n \n \n \n "," \n \n \n \n \n \n EE 107 Fall 2017 Lecture 5 Serial Buses \u2013 UART & SPI\n \n \n \n \n "," \n \n \n \n \n \n Input\/Output and Communication\n \n \n \n \n "," \n \n \n \n \n \n Chapter 10 Input\/Output Organization\n \n \n \n \n "," \n \n \n \n \n \n Diagram of microprocessor interface with IO devices\n \n \n \n \n "," \n \n \n \n \n \n Serial I\/O and Data Communication.\n \n \n \n \n "," \n \n \n \n \n \n SERIAL PORT PROGRAMMING\n \n \n \n \n "," \n \n \n \n \n \n Interrupts, Counter and Timers\n \n \n \n \n "," \n \n \n \n \n \n ATMEGA 32 CONNECTIONS TO RS232; UDR AND UCSR REGISTERS\n \n \n \n \n "," \n \n \n \n \n \n 1 Input-Output Organization Computer Organization Computer Architectures Lab Peripheral Devices Input-Output Interface Asynchronous Data Transfer Modes.\n \n \n \n \n "," \n \n \n \n \n \n E3165 DIGITAL ELECTRONIC SYSTEM\n \n \n \n \n "," \n \n \n \n \n \n Atmega32 Serial Programming Basics\n \n \n \n \n "," \n \n \n \n \n \n The PIC uCs PIC Microcontroller and Embedded Systems Muhammad Ali Mazidi, Rolin McKinlay and Danny Causey Eng. 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Of Gaza 11-1.\n \n \n \n \n "," \n \n \n \n \n \n Computer Organization and Design\n \n \n \n \n "," \n \n \n \n \n \n Introduction to Microprocessors and Microcontrollers\n \n \n \n \n "," \n \n \n \n \n \n USART Universal Synchronous Asynchronous Receiver Transmitter\n \n \n \n \n "," \n \n \n \n \n \n UART Serial Port Programming\n \n \n \n \n "," \n \n \n \n \n \n UART Serial Port Programming\n \n \n \n \n "," \n \n \n \n \n \n Serial Communication Interface: Using 8251\n \n \n \n \n "," \n \n \n \n \n \n Serial Communication Interface\n \n \n \n \n "," \n \n \n \n \n \n UART Protocol Chapter 11 Sepehr Naimi\n \n \n \n \n "," \n \n \n \n \n \n COMP3221: Microprocessors and Embedded Systems\n \n \n \n \n "," \n \n \n \n \n \n PIC18 Timer Programming \u201cExplain the assembly language programming for the timer and counter module\u201d\n \n \n \n \n "," \n \n \n \n \n \n ADC and DAC Data Converter\n \n \n \n \n "," \n \n \n \n \n \n CHAPTER SERIAL PORT PROGRAMMING. Basics of Serial Communication Computers transfer data in two ways: \u25e6 Parallel \uf096 Often 8 or more lines (wire.\n \n \n \n \n "," \n \n \n \n \n \n PIC18 Interrupt Programming\n \n \n \n \n "," \n \n \n \n \n \n EUSART Serial Communication.\n \n \n \n \n "," \n \n \n \n \n \n Prof Afonso Ferreira Miguel\n \n \n \n \n "," \n \n \n \n \n \n PIC Serial Port Interfacing\n \n \n \n \n "," \n \n \n \n \n \n ADC and DAC Data Converter\n \n \n \n \n "," \n \n \n \n \n \n 8051SERIAL PORT PROGRAMMING\n \n \n \n \n "," \n \n \n \n \n \n Figure Serial versus Parallel Data Transfer\n \n \n \n \n "," \n \n \n \n \n \n PIC Serial Port Interfacing\n \n \n \n \n "," \n \n \n \n \n \n PIC18 Interrupt Programming\n \n \n \n \n "]; Similar presentations 2ff7e9595c