Pic18f serial communication examples

The bit is made set for synchronous mode and is cleared for asynchronous mode. BRGH- Configured to determine the asynchronous communication, set for high speed and clear for low speed. TRMT — Status read-only bit shows the status of transmit shift register. The bit is set when a transmission is complete and gets cleared when a transmission is in progress. TX9- This bit is set to high while sending 9-bit long data set for 9-bit data and cleared for 8-bit data.

Tx and Rx pins. Set to enable the port and is cleared to disable the serial port. RX9- This bit is used when 9-bit long data is to be received. The bit is set to select 9-bit reception cleared to select 8-bit reception. SREN — This bit is used only in synchronous mode. CREN — Set to enable continuous reception. Clearing this bit will stop reception. In Embedded Systems, Telecommunication, and Data Transmission applications, Serial Communication is known to be the process of sending data one bit at a time bit-by-bit sequentially, over the serial bus.

It takes a complete clock cycle in order to transfer each bit from an end to the other. Conversely, parallel communication is known to be the process of sending several bits, even bytes, as a whole only in a single clock cycle. However, even if you transfer fewer data per cycle with a serial transmission, you can do it at much higher frequencies which results in higher net transfer rates than of the parallel communication.

There do exist many serial communication protocols, each of which is working in a different way. However, it turns out to be some similarity that they do share in common. Shift registers are used to shift out the data to be transmitted bit-by-bit each clock cycle. Shift registers are basically some D-Flip-Flops serially connected while sharing the same clock line.

Here is a graphical animation that demonstrates how does a shift register work internally. It takes only 1-clock to transfer a single bit, which means it takes 8-clocks for a single byte transfer. 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!

One at the transmitter device and the other at the receiver device. The serial bus consists of a couple of wires data, and clock. As you might have noticed, it takes 4-clocks to send the 4-Bit data from the transmitter to the receiver. In fact, there are some other options and configurations for each serial communication protocols.

Which includes, various data transmission rates, error detection, and correction mechanisms, and much more that adds to the overall complexity associated with each protocol. And conversely, the parallel communication is the process of sending multiple bits, even bytes, as a whole in a single clock cycle. A very basic implementation, that you can create on your own, for the parallel data transfer is shown down below. Here is an animation that shows you how parallel data transfer is done.

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.

There are countless situations in which we do use one or more of the serial communication protocols. Hence, any application will, hopefully, possibly fall under the umbrella of the following purposes. Serial communication protocols are of fundamental importance for each embedded systems application.

And as embedded systems engineers, we must have a very solid experience with almost all of the commonly used serial communication protocols.

There are many serial communication protocols that are existent and being used in various domains and sub-domains of embedded systems. Here is a list of the most common serial communication protocols in the industry.

There is a couple of io pins dedicated to the UART serial communication module highlighted in the following figure. There are actually two forms of UART as follows:. The Synchronous type of transmitters generates the data clock and sends it to the receiver which works accordingly in a synchronized manner.

On the other hand, the Asynchronous type of transmitter generates the data clock internally. There is no incoming serial clock signal, so in order to achieve proper communication between the two ends, both of them must be using the same baud rate.

The baud rate is the rate at which bits are being sent bps bits per second. Technically, NO! The communication over the UART bus can be configured set to be on one of the following modes:. The UART serial communication bus can only have 2 devices communicating with each other in one of the 3 modes shown in the previous sub-section.

Which necessarily means, each device can either be a transmitter or a receiver during the data transmission process. You should know that the transmitter in synchronous mode must generate the serial data clock for the receiver. On the other hand, in asynchronous mode, there is no need to do so. Frankly speaking, the 2-wires are basically crossed! In the idle state, UART lines are pulled high. This allows the receiver side to recognize that there is a transmitter device on the other end which is connected to the serial bus.

To start data transfer, the transmitting UART pulls-down the transmission line from high to low for one clock cycle. When the receiving UART module detects the high to low voltage transition, it begins reading the incoming bits of the entire data frame at the same frequency of the specified baud rate. These are the actual data bits being transmitted from transmitter to receiver. The length of the data frame can be anywhere between 5 and 9 9-Bits if parity is not used and 8-Bits if parity is used.

In general settings, the LSB is the first bit to be shifted-out, transmitted, unless otherwise specified. Parity bit allows the receiver to check the correctness of the received data.

Parity is a low—level error checking mechanism and has two different options to choose from: Even Parity and Odd Parity. After the receiver UART reads the data frame, it counts the number of bits with a value of 1 and checks if the total value is an even or odd number.

If the parity bit is a 0 even parity , the number of bits with a value of 1 in the data frame should sum-up to an even number. If the parity bit is a 1 odd parity , the number of bits with a value of 0 in the data frame should sum-up to an odd number. When the parity bit matches the data, the receiver UART knows that the transmission was a success. As the name suggests, this bit is used to signal the end of the data packet being sent. The sending UART drives the data transmission line from low to high for at least two-bit durations but most often only one bit is used.

The data line is held high back to the idle state and ready for any future transmission. The Baud Rate specifies how fast the data is sent over the bus and it is specified in bits-per-second or bps. You can actually choose any speed for the baud rate.

However, there are some specific values that are known to be the industry standards. The most common and widely-used standardized value is Other standard baud rates include: , , , , , and Obviously, baud rates are always multiples of Baud rates higher than bps can be used with an additional probability of having, at best, missing data packets.

The baud rate is pre-determined and pre-configured by us the programmers in order to match the design specifications. All in all, the transmission process is as simple as you might be thinking right now. The data recovery block is actually a high-speed shifter, operating at x16 times the baud rate. Whereas the main receiver serial shifter operates at the bit rate or at F OSC.

If the transfer is complete, the flag bit, RCIF , is set. Flag bit RCIF is a read-only bit which is cleared by the hardware. There are actually many different standards that utilize the same UART protocol previously described. Both logic-1 and logic-0 are represented by 5V and 0V respectively. The pinout of the DB-9 and their functions are shown down below. The USART can be configured as a full-duplex asynchronous system that can communicate with peripheral devices, such as CRT terminals and personal computers, or it can be configured as a half-duplex synchronous system that can communicate with sensors, modules, etc.

It is a dedicated 8-bit baud rate generator. Down below is the formula for computation of the baud rate for different USART modes which only apply in Master mode internal clock. From this, the error in baud rate can be determined. Here is a snapshot for this table. This ensures the BRG does not wait for a timer overflow before outputting the new baud rate. Enough of general information about UART! The transmitter and receiver are functionally independent but use the same data format and baud rate.

The baud rate generator produces a clock, either x16 or x64 of the bit shift rate, depending on bit BRGH. Parity is not supported by the hardware but can be implemented in software and stored as the ninth data bit. Asynchronous mode is stopped during Sleep. Asynchronous mode is selected by clearing bit SYNC. The TSR register is not loaded until the Stop bit has been transmitted from the previous loading process. No interrupt logic is tied to this bit so the programmer has to poll this bit in software to determine if the TSR register is empty or not.

Transmission is enabled by setting enable bit, TXEN. Normally, when a transmission is first started, the TSR register is empty. A back-to-back transfer is thus possible, which means we can send consecutive data frames continuously as shown in the following diagram.

Clearing the enable bit TXEN during a transmission will cause the transmission to be aborted and will reset the transmitter.

If it feels overwhelming, stay cool. It really does! Each of us has been at the same point and yes! Take the time to understand each step of the mechanics.

Down below are the exact brief steps that you should follow to configure your UART Asynchronous Transmitter, even without looking up any diagram in the datasheet. However, you should consider doing so sooner or later at some point. Using the High-Speed baud rate even for low speeds is advantageous due to the fact that the error percentage will be significantly smaller.

Doing so requires setting the BRGH bit. Using the baud rate formula shown earlier. Therefore, the c-code for this step is as follows. This is done by setting the TXEN bit. Mission Complete! Transmission is done! You can easily use those 3-functions within your code. Down below are the exact brief steps that you should follow to configure your UART Asynchronous Receiver, even without looking up any diagram in the datasheet.

Hence, the c-code for this step is as follows. Step2 Enable the asynchronous serial port. The ISR routine should read out the data from the buffer and store it in the respective safe place.

This action will automatically set the receiver to be ready for a consecutive data reception. Make sure the pin is set as IO. So its up to the user to check for. Read the datasheet and you should be able to disable the particular peripherals like ADC channel. MotoMike Check Table of 18F46k22 the chip you are using. In order to set as RX pin you need to disable Analog input. I have switched to 18F46K22 now.

I get no break point action if I set a break point at the entry of the interrupt? It even runs in Debug with the ICD3. Your example helped me very much. I was having troubles with finding out how to use the functions.

The Peripheral Manual need examples for each function? I will try your other examples! I have done this asy but not in C! I just loaded XC8 yesterday, so I have made lots of progress. Thanks for the tutorial.

But by using those Peripheral Library we are keeping ourselves away from learning how the code works behind those functions specified in the header file. It will be so helpful if you make another tutorial on adc,usart,timer without using those library but by specifying the values of individual registers. I do agree with you, but the whole reason for using Peripheral Library plib is because there are enough tutorials on the internet that do not use plib. If you search for programming PIC with assembly, you will get everything you need to know at register level.

In fact microchip website has sample codes for PIC18 in assembly and non plib based C code. Search microchip website and you find all the things you need to know. So when I do a project I just pick code from here and save time. Just made it public so people can use it if they need to.

Thanks for taking time to make a comment. According to the datasheet both TRIS should be set to 1. I was not able to perform software uart using c18 library. Can you share a tutorial or example projects about software uart.

Great tutorial! I was using code above for pic16LF When I compile, I get an error of undefined symbol. Thanks for the above examples Singular Engineer, I found them very helpful when looking for an example implementation of usart. I know I was…. Nickolas, thank you for taking time to write a comment.

There have been days when I spent hours figuring out. But once a person gets comfortable its a flow! Have a happy PIC Programming! So you may not be able to use those functions. If you still want something that easy, try the free version of mikroe. They got a nice library with examples.

Thanks for helping me. Okay so after some arduous trouble shooting, I decided to start over and just create a new project. I guess I must have messed up some default setting because in the new project it compiles fine. Thank you though, and thanks again for posting this tutorial! SingularEngineer, Thank you so much for posting this tutorial.

What do I need to change or include to have this constant defined? Please help. Thanks again, Erik. On top of that it did fail to resolve according to the IDE but did compile right after changing include path correctly and I got my USART bluetooth module to speak to my computer, so all is now good.

Thanks for the help! Ha ha.. Are you using Windows? Anyways good to know it works. Jordan, do you document your project? If so please share the link here so that people might know your project. If not, then please start documenting and put it in a blog. Did you mean include usart. If so I have that already, and if I look through that file in the project all of the code is greyed out. So I seem to be missing what ever include would define the usart version.

I tried to include the pic18f Any other suggestions? I think I might be getting what you are saying. Is that what it is saying but still compiling? Its bug that is still being worked upon I agree it is annoying. You can fix that by. Hello Singular Engineer, thank you for the code examples. Reading your posts helps get things working much faster than if I were to go at it alone. However, I am still having some issues.

I am using xc8 compiler for a pic18f micro. Maybe I am missing some sort of includes?