How a keyboard sends a letter

Under each key is a switch. Pressing the key closes the switch, or, on some designs, changes a capacitance the electronics can sense. The keycap is only a handle. The switch is the signal.

The switches are wired in a grid of rows and columns, not with a separate wire for every key all the way to the computer. A controller scans the grid many times a second. It asks each row, in turn, which columns have closed. The crossing point identifies the key.

A grid of switches

The controller sends a scan code, a number that means this physical key, not the letter printed on it. The letter can change with the language of the computer. The scan code for the key in that position stays the same.

A press and a release are different events. If the controller sent the code only once, a held key would type one letter. If it repeated too freely, a brief press would type many. The operating system applies a repeat delay and a repeat rate.

From code to character

Software then maps the scan code through the keyboard layout. On a UK layout the same key that types a quote mark on a US layout can type @. The hardware did not change. The map did.

A wireless keyboard does the same scanning locally and sends the codes by radio to a receiver. The cable, or the radio, carries numbers. It does not carry ink.

A grid of switches

A keyboard is a grid of switches. A chip notes which switch closed and sends a code, and the computer turns that code into a character. Under each key is a switch. Pressing the key closes the switch, or, on some designs, changes a capacitance the electronics can sense.

Put those two statements side by side. The first sets the condition. The second says what happens once that condition is met. How a keyboard sends a letter needs both. Drop the first and the second has nothing to explain. Drop the second and the first is only the scene.

From code to character

Pressing the key closes the switch, or, on some designs, changes a capacitance the electronics can sense. The keycap is only a handle.

The order is the explanation. What the first sentence names has to be there before the result in the second sentence can show up. The piece does not ask you to accept the result first and hunt for a cause afterwards.

A check you can make

The keycap is only a handle. The switch is the signal.

A fair check is sequential. Confirm the first statement. Then see whether the second is the result of it, rather than a separate fact parked in the same piece. If the result shows up without the condition, this account does not cover what you are looking at.

The limit of the claim

The switch is the signal. The switches are wired in a grid of rows and columns, not with a separate wire for every key all the way to the computer.

The two statements do different jobs. One says what is there, what it is made of, or what acts on it. The other says the change that follows. The title names the change. It is not an inventory of parts.

The same steps, in order

The switches are wired in a grid of rows and columns, not with a separate wire for every key all the way to the computer. A controller scans the grid many times a second.

Nothing in the second statement cancels the first. It carries the first forward or marks the limit of it. Remember only the result, and the cause goes missing. Remember only the cause, and you will not know what the piece says happens next.

Why the order matters

A controller scans the grid many times a second. It asks each row, in turn, which columns have closed.

Read them as one path. Start at the first full stop and do not skip to the outcome. The words between the two statements are the mechanism. The title is the name of that path, not a second claim.

Condition, then outcome

It asks each row, in turn, which columns have closed. The crossing point identifies the key.

The first statement can be true and still not finish the job. The second statement is the job finishing. Hold both, and the paragraph above stops being a list. It becomes the reason the title is worded as it is.

What the title is naming

The crossing point identifies the key. The controller sends a scan code, a number that means this physical key, not the letter printed on it.

If you wanted a shorter version, it would be those two sentences and nothing else. Everything added around them is there so the dependence is obvious: the second does not happen unless the first has happened.

What has to come first

The controller sends a scan code, a number that means this physical key, not the letter printed on it. The letter can change with the language of the computer.

Put those two statements side by side. The first sets the condition. The second says what happens once that condition is met. How a keyboard sends a letter needs both. Drop the first and the second has nothing to explain. Drop the second and the first is only the scene.