Software 5. Project Takeaways 6. Fundamental Concepts 6. Asynchronous Communications 6. UART Hardware 6. UART Software 7. Background Information 8. Lab 4b. Lab 4c. Lab 4d. Control the stepper motor speed and direction of rotation using commands entered from a terminal emulation program. Basys MX3 trainer board. Digilent Analog Discovery 2. Understanding of the basics of telecommunications. How to develop a library of PIC32 software to provide bi-directional communications of single characters and strings of characters.
See the general discussion concerning computer communications discussed in Unit 4 Part 1. Communications Speed: BAUD is a unit used to measure the speed of signaling or data transfer, equal to the number of pulses or bits per second, or baud rate.
Stop Bits: Only one is necessary for the receiving device. The sending device has the option of sending one or two minimum stop bits. Bus Idle: This is the nominal state of the data signal when no data is being transmitted.
The idle condition is a logic level 1 or high condition. The bus idle condition is an extension of stop bits; however, the period bus idle condition may be any time duration.
Even parity refers to a parity checking mode in asynchronous communication systems in which an extra bit, called a parity bit, is set to one if there is an odd number of one bits in a one-byte data item.
Odd parity refers to a parity checking mode in asynchronous communication systems in which an extra bit, called a parity bit, is set to one if there is an even number of one bits in a one-byte data item. This configuration is known as a bus configuration. USB is a complex protocol that can support many different classes of devices, from human interface devices HID like mice and keyboards to mass storage devices to cameras, and more.
Devices that include a USB-to-serial converter will show up as serial ports to your computer when you plug them in. Many microcontroller boards, including the Arduino boards, include a USB-to-serial converter to communicate with your computer in this way. When you plug them in, any program that can read serial ports will list the connected Arduino in the list of serial ports. The process is slightly different on the different microcontrollers, but there are some elements common to all of them.
All processors that have a UART this includes personal computers and microcontrollers, and most embedded boards like the Beaglebone Black and Raspberry Pi as well have an area in memory where they store incoming data from the serial ports called a serial buffer.
Because of this, they can do other tasks while waiting for data to come in, and act on the data from the buffer after it comes in.
Serial ports can only be controlled by one program at a time. On computers with an operating system, you might have multiple programs running, but only one can control a given serial port at any one time. Related video: Only one program can control the port. As you read each byte, the byte is removed from the serial buffer. Even worse, for bps, it is 3. The reason for these deviations has been already mentioned: The AVR baud rate generator cannot generate all rates.
The next interesting observation is that SoftwareSerial should probably not be used with bit rates above bps. Similarly, AltSoftSerial does refuse to work when a bit rate higher than bps is requested. The clear winner appears to be picoUART. So, how do the libraries fare when they shall receive data? I used the following sketch a bit simplified to test the performance of SoftwareSerial. For the other libraries, it looks similar. Notice that I do not use the available method, but I simply read and ignore the result when it is less than zero.
That is the fastest way to read bytes coming over a stream. The data to be received is generated by a Python script that drives a FTR board.
The FTR can generate almost any bitrate you want. It will select a bitrate that is as close as possible to one that leads to an integer result when dividing 24 million by the bitrate. Here is the simplified script. You call it with the following parameters:. The script changes the bitrate systematically by permille steps and stops when the Arduino sketch pulls the CTS line down because it reads an unexpected byte.
For some bitrates, the libraries gave an error when the millis interrupt was active, which is not a big surprise, given that the interrupt latency of 6.
Sometimes, the idle time between reading two bytes was too short. I allowed for some extra time by using a sending format with 2 stop bits. This is marked by a star in the table. For each library, I report the maximal negative and positive relative deviation that the library tolerated. I tested it with at least 10, bytes. For all bitrates above 10, bps, I tested it with , bytes. And for all bitrates higher or equal to , bps, I used 1 million bytes.
The reported percentages are those that are tolerated, while the next higher or lower bitrate led to an error. Note that in particular with higher bitrates, the step to the next bitrate can be quite large e. Finally, one should note that I used the blocking variant of picoUART, which blocks interrupt once the read routine is called. There are a number of interesting results in this table. First, in general, it is obvious that the hardware UART is the most robust, which is not a big surprise.
There are two things to note, though. It is completely unclear to me why the hardware UART does not have a symmetric tolerance interval. So why does it at nominal bps tolerate a bitrate that is 5. I have no idea! The two handshaking lines are data valid, which is generated by the source unit, and data accepted, generated by the destination unit. The timing diagram shows the exchange of signals between the two units. The sequence of events listed in part c shows the four possible states that the system can be at any given time.
The source unit initiates the transfer by placing the data on the bus and enabling its data valid signal. The data accepted signal is activated by the destination unit after it accepts the data from the bus.
The source unit then disables its data valid signal, which invalidates the data on the bus. The destination unit then disables its data accepted signal and the system goes into its initial state. The source does not send the next data item until after the destination unit shows its readiness to accept new data by disabling its data accepted signal.
This scheme allows arbitrary delays from one state to the next and permits each unit to respond at its own data transfer rate. The rate of transfer is determined by the slowest unit. The destination-initiated transfer using handshaking lines is shown in Fig. Note that the name of the signal generated by the destination unit has been changed to ready for data to reflect its new meaning.
The source unit in this case does not place data on the bus until after it receives the ready for data signal from the destination unit. From there on , the handshaking procedure follows the same pattern as in the source-initiated case. Note that the sequence of events in both cases would be identical if we consider the ready for data signal as the complement of data accepted. In fact, the only difference between the source-initiated and the destination-initiated transfer is in their choice of initial state.
The handshaking scheme provides a high degree of flexibility and reliability because the successful completion of a data transfer relies on active participation by both units. If one unit is faulty, the data transfer will not be completed. Such an error can be detected by means of a timeout mechanism, which produces an alarm if the data transfer is not completed within a predetermined time.
The timeout is implemented by means of an internal clock that starts counting time when the unit enables one of its handshaking control signals. If the return handshake signal does not respond within a given time period, the unit assumes that an error has occurred.
The timeout signal can be used to interrupt the processor and hence execute a service routine that takes appropriate error recovery action. The transfer of data between two units may be done in parallel or serial. In parallel data transmission, each bit of the message has its own path and the total message is transmitted at the same time. This means that an n-bit message must be transmitted through n separate conductor paths.
In serial data transmission, each bit in the message is sent in sequence one at a time. This method requires the use of one pair of conductors or one conductor and a common ground.
Parallel transmission is faster but requires many wires. It is used for short distances and where speed is important.
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