Category: Uart fpga4fun

Uart fpga4fun

This post goes over setting up the examples and explains some of the code. The accelerometer puts out 16 bits of data for each of the three dimensions.

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The accelerometer verilog code comes from Terasic, but with a modified module which includes the 2-bit input register called dimension. When dimension is 0, the axis to be read is x, 1 is y and 2 is z. Both examples use a simple state machine to handle responding to incoming signals.

It looks like this:.

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To load the DE0-Nano, can either import the verilog and tcl files into your own quartus project, or use my pyquartus tool. To compile and upload using pyquartus, plug your DE0-Nano into your computer, and run:. On the raspberry pi side, install the requirements and run the program by opening up a terminal and running the commands:. The serial verilog code was adapted from Jean P Nicolle at fpga4fun. The example requires two state machines - one to handle the transitions between read to write, one to handle setting the output data.

On the parallel example, the Raspberry Pi does the heavy lifting. It uses a pin for clock, a pin to indicate whether the data pins are being used for reading and writing, and then 8 pins for data. This is accomplished using the RPi. GPIO python library:. In verilog, the code is pretty simple and can be accomplished with a ternary operator and some logic triggered by the clock:. I use the negative edge of the clock signal to ensure the data pins on the Raspberry Pi are synchronized and ready.

The serial example can transmit at baud, however, after about a second of communication, the Raspberry Pi and FPGA stop communicating. In both of these cases, it might be possible to get faster and more reliable performance by switching to c. Toggle navigation Catherine's Auxiliary Brain.Data is commonly sent by chunks of 8 bits we call that a byte and is "serialized": the LSB data bit 0 is sent first, then bit 1, This interface uses an asynchronous protocol.

That means that no clock signal is transmitted along the data.

uart fpga4fun

The receiver has to have a way to "time" itself to the incoming data bits. Byte 0x55 is in binary. But since it is transmitted LSB bit-0 first, the line toggles like that: Here the data is 0xC4, can you see it? The bits are harder to see. That illustrates how important it is for the receiver to know at which speed the data is sent.

uart fpga4fun

The speed is specified in baud, i. For example, bauds would mean bits-per-seconds, or that each bit lasts one millisecond. Common implementations of the RS interface like the one used in PCs don't allow just any speed to be used. If you want to use bauds, you're out of luck.

You have to settle to some "standard" speed. Common values are:. If you transmit 8-bits data, that lasts 8 x 8. But each byte requires an extra start and stop bit, so you actually need 10 x 8. That translates to a maximum speed of At bauds, some PCs with buggy chips require a "long" stop bit 1. Allows bidirectional full-duplex communication the PC can send and receive data at the same time.

DB-9 connector You probably already saw this connector on the back of your PC. It has 9 pins, but the 3 important ones are: pin 2: RxD receive data. Using just 3 wires, you can send and receive data.

Asynchronous communication This interface uses an asynchronous protocol. In the case of RS, that's done this way: Both side of the cable agree in advance on the communication parameters speed, format That's done manually before communication starts. The 8 bits of the byte data are sent.

Let's see how looks the byte 0x55 when transmitted: Byte 0x55 is in binary. Here's another example: Here the data is 0xC4, can you see it? How fast can we send data? Common values are: bauds. So an idle line carries something like V.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts.

It only takes a minute to sign up. According to it the standard practice for asynchronous communication is to oversample the signal at 16 times the BAUD rate. This makes sense to me since I would need to do this to detect the first drop quickly and synchronize with the transmitting clock.

Is there any harm in doing this? I know it would probably just consume more power, but would it work or is there something I am missing? I've sampled at 8 times on one job and it was OK so there is no rule dictating that 16 is the magic number so sampling higher than this is not a problem in anthing other than handling bigger numbers in hardware.

Here's a the 16x counter idea:. From the falling edge of the start bit you "find" the start-bit's "middle" by counting to 8 then, each count of 16 thereafter you "sample" the UART received data to recreate the byte or bytes transmitted. Clearly if you had a 32x counter you'd get a tad more accuracy in determining the centre-point of the bit and counting at a higher rate is going to work but the numbers get bigger and the power consumption rise.

However, many UART designs need to be both robust and flexible, and that drives the design toward creating a 16x clock or clock enable signal. For robustness, it is advantageous to sample each bit multiple times near the center of the bit and then take a vote among the multiple samples in order to minimize the effects of noise. If you tried to take three adjacent samples at MHz, they're almost guaranteed to have the same value even if they are a glitch, so you want them spaced farther apart.

For flexibility — for example, needing to support many different possible baud rates — you want to have just one parameter that controls the baud rate. If you have several different internal delays that depend on the baud rate i. In that case, all of the different delays scale with the one parameter automatically.

There is a lower boundary for over-sampling defined by the the possible error made by missing the falling edge of the start bit. So by a 8x over-sampling a possible mismatch of the falling edge causes an max. The upper boundary is limited by your investment in hardware ressources. No one wants to use a 32 bit counter :. Sign up to join this community.

The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 4 years, 3 months ago. Active 4 years, 3 months ago.

Driving a VGA Display?! Getting started with an FPGA! (TinyFPGA)

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Here's a the 16x counter idea: - From the falling edge of the start bit you "find" the start-bit's "middle" by counting to 8 then, each count of 16 thereafter you "sample" the UART received data to recreate the byte or bytes transmitted. Andy aka Andy aka k 14 14 gold badges silver badges bronze badges. Then one data cell is usec.So in this way the 12v serial level signal are converted to 5v and vice versa to work compatible with FPGA.

Then i have implemented uart code in FPGA to manipulate recieved and transmitted signals.

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Now i want to do same with the RJ45 ethernet port to achieve a higher speed of 10 Mbps. Am i correct?

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The fpga4fun method might work, but it's not great. It would be embarrassing to include it in anything other than a hobby project.

QFN chips are not much of a problem to hand-assemble, but if you want something easier you might want to consider:. DIP chips are pretty rare these days and Ethernet interfaces tend to tie up lots of pins.

Stick to one of these modules if you want 10baseT.

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If you want anything faster, consider buying a new development board that already includes a PHY. If you're designing your own board, skip the DIP and learn how to assemble with SMT parts - pretty much everything interesting these days is surface mount! You could use LVDS inputs and a transformer, but don't expect to get metres.

If you have to ask us these questions, it's almost certainly unsafe for your FPGA and the other devices you're connecting up. PHYs incorporate protection devices that are designed to withstand the requirements of the various Ethernet standards. Xilinx FPGAs don't implement the required voltage standards. You have mentioned a few different implementation schemes, but you haven't described the design requirements. Perhaps with a 'problem description' we might be able to suggest a simple and safe solution.

Both are 20 meter apart. Do you understand the importance of details which you waited until post 6 to reveal? Sign In Help. Turn on suggestions. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type. Showing results for. Search instead for. Did you mean:.


All forum topics Previous Topic Next Topic. Before answering, what is the real question? What bit rate? Transmit only, or transmit and receive? What distance? Maximum number of cable conductors? FPGA at the other end of the link? Read the manual or user guide.Here we want to use the serial link at maximum speed, i. We need to find a way to generate from the FPGA clock a "tick" as close as possible to times a second. Traditionally, RS chips use a 1. That was easy.

But what do you do if instead of 1. To generate Hz from a 2MHz clock, we need to divide the clock by " The solution is to divide sometimes by 17, sometimes by 18, making sure the ratio stays " That's actually easy to do. It is desirable that the be a power of two. Obviously is not. So we change the ratio That's very close to our ideal ratio, and makes an efficient FPGA implementation: we use a bit accumulator incremented by 59, with a tick marked everytime the accumulator overflows.

Using our 2MHz clock, "BaudTick" is asserted times a second, a 0. The previous design was using a 10 bits accumulator, but as the clock frequency increases, more bits are required. Here's a design with a 25MHz clock and a 16 bits accumulator. The design is parameterized, so easy to customize. One last implementation issue: the "BaudGeneratorInc" calculation is wrong, due to the fact that Verilog uses 32 bits intermediate results, and the calculation exceeds that.

Change the line as follow for a workaround. Now that we have a precise enough Baud generator, we can go ahead with the RS transmitter and receiver modules. Parameterized FPGA baud generator The previous design was using a 10 bits accumulator, but as the clock frequency increases, more bits are required.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. I don't know if this belongs here or stackoverflow. I assume here as although verilog looks like software it's actually describing hardware connections?

I have a Spartan-3AN evaluation board and I'm trying to implement a simple rs port interface on it which I can't get to work. I'm an experienced software developer but new to verilog and digital design. I want to move up from flashing a single LED to the next step. I've tried to implement it like this - 1 Generate a clock pulse "serclock" at the baud rate, so at the start of each bit. If there is a better way I'd appreciate any help.

However I would expect this to work but I get nothing at all. Can anyone spot anything stupid that I've done? I'd appreciate any advice. I don't speak Verilog, but I noticed that your stopbit is zero, which should be 1.

Are you reading the port on a scope, or are you reading on a UART? In the latter case you may not have a character received if it doesn't see the stopbit. That said, I assume that you are doing this to learn Verilog? Otherwise, there are many freely available cores that you can find on the Internet that does this. Sign up to join this community. The best answers are voted up and rise to the top.

Home Questions Tags Users Unanswered. Implement serial port on fpga verilog Ask Question. Asked 8 years, 11 months ago. Active 6 years, 10 months ago. Viewed 12k times. Kevin Vermeer John Burton John Burton 1, 3 3 gold badges 22 22 silver badges 33 33 bronze badges.

The problem is that I get nothing at all on the serial port output. That's all it was.


I looked at that code times and didn't notice. Thank you, it works perfectly now. Can you put this as an answer then I can accept it? Your code is almost certainly functional, but could use some review by experienced designers. First suggestion I'd make is that where you generate outbit you could use a shift register rather than a mux to reduce resource usage.

Active Oldest Votes. Seemed like a nice manageable little project to learn some basics.

uart fpga4fun

I figured that the clock would wrap around soon enough anyway though so this would just cause the first bit to be delayed a few ms.Once again I'm sorry if I'm asking what can be considered silly questions, but I'm diving into the FPGA world by myself and I'm having serious dificulties finding documentation or examples that fit my questions. I've seen some examples of UART implementations, some I found in responses here on the forum, but due to my lack of knowledge it seems to me they lack important things so I could understand them.

So I'll ask two questions:. But how do I define the adress of that register? I haven't been able to find any example for this.

This will help you get past your XDC questions as well. You can find my example project doing just this thing on github. Please consider this seriously. FPGA's are difficult enough to deal with. This wasn't why you bought your FPGA board, now, was it? But to come back and answer your question, registers are assigned typically by the bus interconnect structure. I'll repeat my answer to another post to reply to your question I would suggest to start with a simpler design and work up to this more complex project.

I would also suggest looking at the fpga4fun. And the reason why I'm working with a FPGA is because my instructor wants me to use one in my thesis, with a microcontroller it would be much easier and probably would be done by now. One of the sad realities of a serial port is that one chips receiver is another's transmitter. Sometimes when the schematic calls it a receiver, it's a transmitter with respect to the FPGA chip, other times it's a receiver.

I have then used this link in the past to build a GUI, although it was terribly slow. One of the difficulties you will see across this forum with using the MicroBlaze microcontroller, is that 1 there are only a limited number of caned demos, 2 going beyond the canned demos isn't very clear, and 3 it's very difficult to debug when things go wrong--especially since you have no insight into what the micro is doing.

On the other hand, if you started with an open source microcontrolleryou'd have everything at your fingertips in order to debug it. Just something to think about. Let me try explaining this another way. If you are familiar with software, and have a strong software background it sounds like you dothen you can usually debug things via printf.

FPGA's, however, are notoriously difficult to debug by printf. Yes, it is possible to debug the micro by printfbut not until 1 you have it up and running, and 2 your peripherals are work. As an example, on a recent design I was working on I messed up the the connection between a component and the system bus. I say this to point out that it isn't that uncommon.

What was wrong with my design? Debug by printf wouldn't work. Well perhaps. But this comment does put a different perspective on things. Could it be that your instructor believes that FPGA development is a software project? I'd certainly argue against such a proposition. For someone hoping to complete a project using a platform requiring a whole level of skills unnecessary to the job I feel your pain. As someone who has used that and prefers HDL I don't agree that doing this and adding a Microblaze is necessarily easier or quicker.

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