I have some nodes that are connected to a server with RS485. I use stm32f103 microcontroller with MAX485 in nodes. We use modebus connection. The driver is connected to a nano pi m3 as server. The baudrate is 115200.
The problem is that sometimes I lose a node. It means that I don't receive any data, not a wrong data. There is also no pattern, for example one day I don't receive data from first node and the other day I don't have data of the 3rd one. If it helps, I reset the system by unplugging it every day. Also the address of each node is identical.
I used a shielded twisted pair for rs485 and I connected the ground of nodes to the ground of driver. I also used two 120 ohm resistors to terminate the line,
one in driver and the other in the last node, the intermediate nodes do not have any 120 ohm resistors.
The question is that it may be a hardware problem or a software?
Related
I am developing a measurement system, comprised of a MCU (being STM, ESP or PIC), multiple (let's say 8) ADCs sending data over SPI. ADCs are to be triggered using a SYNC signal so that they sample at the same time. It's crucial to access the data at the same time (or almost at the same time), the sampling frequency will be 1 or 2 kHz. I'm wondering how should I approach this: use a single physical SPI bus, and perhaps a DMA, or get a MCU with 8 physical SPI buses allowing them to operate in parallel?
Additionally, I would like this MCU to support Ethernet connection, to send the data to a post-processing unit.
My initial thought was to simply get a MCU with 8 SPIs, but maybe it's an overkill?
I have a STM32F417IG microcontroller an external 16bit-DAC (TI DAC81404) that is supposed to generate a Signal with a sampling rate of 32kHz. The communication via SPI should not involve any CPU resources. That is why I want to use a timer triggered DMA to shift the data with a rate of 32kHz to the SPI data register in order to send the data to the DAC.
Information about the DAC
Whenever the DAC receives a channel address and the new corresponding 16bit value the DAC will renew its output voltage to the new received value. This is achieved by:
Pulling the CS/NSS/SYNC – pin to low
Sending the 24bit/3 byte long message and
Pulling the CS back to a high state
The first 8bit of the message are containing among other information the information where the output voltage should be applied. The next and concurrently the last 16bit are containing the new value.
Information about STM32
Unfortunately the microcontroller of ST are having a hardware problem with the NSS-pin. Starting the communication via SPI the NSS-pin is pulled low. Now the pin is low as long as SPI is enabled (. (reference manual page 877). That is sadly not the right way for communicate with device that are in need of a rise of the NSS after each message. A “solution” would be to toggle the NSS-pin manually as suggested in the manual (When a master is communicating with SPI slaves which need to be de-selected between transmissions, the NSS pin must be configured as GPIO or another GPIO must be used and toggled by software.)
Problem
If DMA is used the ordinary way the CPU is only used when starting the process. By toggling the NSS twice every 1/32000 s this leads to corresponding CPU interactions.
My question is whether I missed something in order to achieve a communication without CPU.
If not my goal is now to reduce the CPU processing time to a minimum. My pIan is to trigger DMA with a timer. So every 1/32k seconds the data register of SPI is filled with the 24bit data for the DAC.
The NSS could be toggled by a timer interrupt.
I have problems achieving it because I do not know how to link the timer with the DMA of the SPI using HAL-functions. Can anyone help me?
This is a tricky one. It might be difficult to avoid having one interrupt per sample with this combination of DAC and microcontroller.
However, one approach I would look at is to have the CS signal created as a timer output-compare (like PWM). You can use multiple channels of the same timer or link multiple timers to create a delay between the CS output and the DMA trigger. You should allow some room for jitter, because depending on what else is happening the DMA might not respond instantly. This won't hurt your DAC output signal though, because it only outputs the value on the rising edge of chip select (called SYNC in the DAC datasheet) which will still be from your first timer.
I'm confused.
I have recently started working on building an operating system while using bochs as an emulator and a certain manual online.
In the manual to move the vga framebuffer cursor I'm using the IO ports using the command 'out'. I get how to control it but I don't know what is it that I'm controlling, and after some reading it seems like everywhere it was addressed as an abstract thing that for example makes the cursor to change its position on the screen.
What I want to know: what are they physically? are they cables? if yes from where to where they are connected? can I input from them also as there name suggest? and why do I need the out command and cant write directly to their place in the memory?
If in your answer you can also include the serial ports and the difference between them and the IO ones it will be amazing,
with respect,
revolution
(btw the operating system is 32 bits)
An IO port is basically memory on the motherboard that you can write/read. The motherboard makes some memory available other than RAM. The CPU has a control bus which allows it to "tell" the motherboard that what it outputs on the data bus is to be written somewhere else than RAM. When you output to the VGA buffer, you write to video memory on the motherboard. The out/in instructions are used to write/read IO ports instead of writing to RAM. When you use out/in instructions, you instruct the CPU to set a certain line on its control bus to tell the motherboard to write/read a certain byte to an IO port instead of RAM.
Today, a lot of RAM memory is used for hardware mapping instead of IO ports. This is often called the PCI hole. It is memory mapped IO. So you will write to RAM and it will send the data to hardware like graphics memory. All of this is transparent to OS developers. You are simply using very abstract hardware interfaces which are either conventional (open source) or proprietary.
Serial ports in the meantime are simply ports which are serial in nature. A serial port is defined to be a port where data is transferred one bit at a time. USB is serial (universal serial bus). VGA is serial and others are too. These ports are not like IO ports. You can output to them indirectly using IO ports.
IO ports offer various hardware interfaces which allow to drive hardware. For example, if you have a VGA compatible screen and set text mode, the motherboard will make certain IO ports available and, when you write to these IO ports, video memory will vary depending on what you output to these ports. Eventually, the VGA screen will refresh when the video controller will output data written to video memory through the actual VGA port. I'm not totally aware of how all of this works since I'm not an electrical engineer and I never read about this stuff. To what I know, you can see the pins of the VGA port and what they do independently on wikipedia. VGA works with RGBHV. RGB stands for red, green and blue while HV stand for horizontal/vertical sync. As stated on wiki in the article on analog television:
Synchronizing pulses added to the video signal at the end of every scan line and video frame ensure that the sweep oscillators in the receiver remain locked in step with the transmitted signal so that the image can be reconstructed on the receiver screen. A sync separator circuit detects the sync voltage levels and sorts the pulses into horizontal and vertical sync.
The horizontal synchronization pulse (horizontal sync, or HSync), separates the scan lines. The horizontal sync signal is a single short pulse which indicates the start of every line. The rest of the scan line follows, with the signal ranging from 0.3 V (black) to 1 V (white), until the next horizontal or vertical synchronization pulse.
Memory in itself takes various forms in hardware. Video memory is often called VRAM (Video RAM) or the Frame Buffer as you can read in a Wikipedia article. So in itself video memory is an array of DRAM. DRAM today is one capacitor (which stores the data) and one mosfet transistor (which controls the flow of the data). So you have special wiring on the motherboard between the data bus of the processor and the VRAM. When you output data to video memory, you write to VRAM on the motherboard. Where you write and how just depends on the video mode you set up.
Most modern systems work with HDMI/Display port along with graphics card. These graphics card are other hardware interfaces which are often complex and they often cannot be known because the drivers for the cards are provided by the manufacturers. osdev.org has information on Intel HD Graphics which has a special interface to interact with. It can be used to gather info on the monitor and to determine what RAM address to use to write to the monitor.
Morning Overflowers,
For a specific in-house application for my company, I need to be able to make a Gigabit ethernet connection go through DB15 connectors, as seen bellow.
Here is what I'm trying to achieve:
For the first version, I just cut in half a cat 5e ethernet cable. I did not care too much about the pin-out from the cable to the DB15 connector and in the end I ended up having a 10MBit/s data rate, which is super low. Also my cable was super short, 2m in total.
For the second version I used a 5m cat 6 cable for one side, and the remain of the other cat 5e cable (resoldered) for the other side. I was more careful about the pinout and used the 4 left most pins to place the ethernet pairs as seen here:
The data rate is this time 100 MBits/s, but still not 1 GBits/s.
Before going through a 3rd version I thought I'd use my brain a little. I noticed while soldering that although inside a cat 5e/cat 6 cable there are 4 pairs, not all of them are side by side on the RJ45 socket as seen on figure bellow where blue and green wires are a bit mixed.
There is probably a reason for that arrangement and putting pairs together other that inside the cable itself is not probably a good idea, which leads to my question.
For version 3, should I just keep pin 1 to 8 in that order and solder them to the DB15 connector on adjacent pins?
More generally I am aware that unless the DB15 section is super short I won't be able to maintain Gibabit ethernet due to noise and other problems caused by unmatched pairs on that section.
I am open to any suggestion or tips or anything :)
Thanks in advance
After trial and errors, it turned out that it works fine if you arrange pairs to match a RJ45 connector (like on the figure "ethernet plug wiring"). The quality of the cable is probably not the one of a perfect 5e/6 cable but my computer can negociate a Gbits connection and transfer files over the network at speeds way above 10 MB/s reaching 50 MB/s. I always soldered more section with various connectors and it worked fine too.
I'd like to send multiple signals (4 inputs and outputs and 7 outputs) from my Laptop to a microcontroller. I'm thinking of using a USB to serial converter and multiplexing the data through the port. I'll need to write codes both in the laptop end and in the microcontroller to multiplex the data.
Eg:
Tx of microcontroller:
1.Temperature sensor ADC output->Laptop
2.Voltage sensor to laptop
3.Current Sensor to Laptop
4.Photodiode current to Laptop
So I need to write a program in the microcontroller to send the data in this order. How can I accomplish this? I was thinking of an infinite loop which sends the data with time delays in between.
At the Rx pin of Microcontroller,
Seven bit sequences. Each bit sequence will be used to set the duty cycle of a PWM generated by the microcontroller.
I also need the same multiplexing or demultiplexing arrangement in the matlab end. Here too, I'm thinking of allotting some virtual 'channels' at different instants of time. What kind of algorithm would I need?
In case you always send all the inputs/outputs at the same rate, you could simply pack them into 'packets', which always start with one or more bytes with a fixed value that form a 'packet header'. The only risk is that one of the bytes of the sensor data might have the same value as the start-byte at the moment you try to start receiving bytes and you are not yet synchronized. You can reduce this risk by making the header longer, or by choosing a start-byte that is illegal output for the sensors (typically OxFF or so).
The sending loop on the microcontroller is really easy (pseudocode):
while True:
measure_sensors()
serial.send(START_BYTE)
serial.send(temperature)
serial.send(voltage)
serial.send(current)
serial.send(photodiode)
end while
The receiving loop is a bit more tricky, since it needs to synchronize first:
while True:
data = serial.receive()
if data != START_BYTE:
print 'not synced'
continue #restart at top of while
end if
temperature = serial.receive()
voltage = serial.receive()
current = serial.receive()
photodiode = serial.receive()
do_stuff_with_measurements()
end while
This same scheme can be used for communication in both directions.