Serial common

That's the main argument against using the comma in every case—leaving it out often doesn't change anything. The serial comma is also sometimes called the Oxford comma because it's used by Oxford University Press or the Harvard comma because it's used by Harvard University Press, but I find these names misleading because so many other publications also use the serial comma.

Using Serial Commas Adds Consistency Although the serial comma isn't always necessary, I favor it because often it does add clarity, and I believe in having a simple, consistent style, instead of trying to decide whether you need something on a case-by-case basis. I also think using the serial comma makes even simple lists easier to read. Really, unless space is incredibly expensive, I can't imagine why anyone would decide the best method is sometimes leave it out and sometimes add it in.

You can make the meaning clear in two ways: place the final comma after peanut butter or after chocolate chip, or rewrite the sentence so that there is no ambiguity. If you want to say that the combination is peanut butter and chocolate chip, you can write blueberry, peanut butter and chocolate chip, and coconut , or if you insist on leaving out the serial comma, you can rewrite the list as peanut butter and chocolate chip, coconut and blueberry.

But I still think the rewrite is more risky than the sentence with the serial comma because a reader who's just skimming the sentence could be tempted to think that coconut and blueberry is a combination.

Another case where leaving the comma out can be confusing is when the later items in the list can describe an earlier item. An oft-cited example is the made-up book dedication To my parents, Ayn Rand and God. A reasonable reader would assume there are four entities being thanked: mom, dad, Ayn Rand, and God; but without the serial comma you could also conclude that the two parents are Ayn Rand and God.

A serial comma clears up any confusion: To my parents, Ayn Rand, and God. It's fast, straightforward, and relatively easy to implement. So, we often opt for serial communication, sacrificing potential speed for pin real estate. Over the years, dozens of serial protocols have been crafted to meet particular needs of embedded systems. USB universal serial bus , and Ethernet, are a couple of the more well-known computing serial interfaces.

Other very common serial interfaces include SPI, I 2 C, and the serial standard we're here to talk about today. Each of these serial interfaces can be sorted into one of two groups: synchronous or asynchronous. A synchronous serial interface always pairs its data line s with a clock signal, so all devices on a synchronous serial bus share a common clock.

This makes for a more straightforward, often faster serial transfer, but it also requires at least one extra wire between communicating devices. Asynchronous means that data is transferred without support from an external clock signal. The serial protocol we'll be discussing in this tutorial is the most common form of asynchronous transfers. The clock-less serial protocol we'll be discussing in this tutorial is widely used in embedded electronics. The asynchronous serial protocol has a number of built-in rules - mechanisms that help ensure robust and error-free data transfers.

These mechanisms, which we get for eschewing the external clock signal, are:. Through the variety of these signaling mechanisms, you'll find that there's no one way to send data serially. The protocol is highly configurable. The critical part is making sure that both devices on a serial bus are configured to use the exact same protocols. The baud rate specifies how fast data is sent over a serial line. It's usually expressed in units of bits-per-second bps.

If you invert the baud rate, you can find out just how long it takes to transmit a single bit. Baud rates can be just about any value within reason. The only requirement is that both devices operate at the same rate. One of the more common baud rates, especially for simple stuff where speed isn't critical, is bps. Other "standard" baud are , , , , , , and You usually won't see speeds exceeding - that's fast for most microcontrollers. Get too high, and you'll begin to see errors on the receiving end, as clocks and sampling periods just can't keep up.

Each block usually a byte of data transmitted is actually sent in a packet or frame of bits. Frames are created by appending synchronization and parity bits to our data. A serial frame. Some symbols in the frame have configurable bit sizes. The real meat of every serial packet is the data it carries. We ambiguously call this block of data a chunk , because its size isn't specifically stated. The amount of data in each packet can be set to anything from 5 to 9 bits. Certainly, the standard data size is your basic 8-bit byte, but other sizes have their uses.

A 7-bit data chunk can be more efficient than 8, especially if you're just transferring 7-bit ASCII characters. After agreeing on a character-length, both serial devices also have to agree on the endianness of their data.

Is data sent most-significant bit msb to least, or vice-versa? If it's not otherwise stated, you can usually assume that data is transferred least-significant bit lsb first.

The synchronization bits are two or three special bits transferred with each chunk of data. They are the start bit and the stop bit s. True to their name, these bits mark the beginning and end of a packet. There's always only one start bit, but the number of stop bits is configurable to either one or two though it's commonly left at one. The start bit is always indicated by an idle data line going from 1 to 0, while the stop bit s will transition back to the idle state by holding the line at 1.

Parity is a form of very simple, low-level error checking. It comes in two flavors: odd or even. To produce the parity bit, all bits of the data byte are added up, and the evenness of the sum decides whether the bit is set or not. For example, assuming parity is set to even and was being added to a data byte like 0b , which has an odd number of 1 's 5 , the parity bit would be set to 1. Conversely, if the parity mode was set to odd, the parity bit would be 0.

Parity is optional , and not very widely used. It can be helpful for transmitting across noisy mediums, but it'll also slow down your data transfer a bit and requires both sender and receiver to implement error-handling usually, received data that fails must be re-sent. So, what would a packet or two of 8N1 data look like?

Let's have an example! The ASCII value of O that's uppercase is 79, which breaks down into an 8-bit binary value of , while K 's binary value is All that's left is appending sync bits.

Notice how each of the two bytes is sent as it reads from right-to-left. For every byte of data transmitted, there are actually 10 bits being sent: a start bit, 8 data bits, and a stop bit. Now that you know how to construct serial packets, we can move on to the hardware section.

There we'll see how those 1's and 0's and the baud rate are implemented at a signal level! A serial bus consists of just two wires - one for sending data and another for receiving. As such, serial devices should have two serial pins: the receiver, RX , and the transmitter, TX. It's important to note that those RX and TX labels are with respect to the device itself. So the RX from one device should go to the TX of the other, and vice-versa. For example:. Real-time suggestions, wherever you write.

Ann Edwards. The Oxford or serial comma is the final comma in a list of things. For example: Please bring me a pencil, eraser, and notebook. I love Lady Gaga, Humpty Dumpty and my parents.