打印機開發中，對ASCII?(American Standard Code for Information Interchange)的熟悉有助于相關概念的理解。同時深入理解ASCII的相關背景，也可以了解計算發展的歷史。在很久以前的機械打字機時代，CR和LF分別具有不同的作用：LF會將打印紙張上移一行位置，但是保持當前打字的水平位置不變；CR則會將“Carriage”（打字機上的滾動托架）滾回到打印紙張的最左側，但是保持當前打字的垂直位置不變，即還是在同一行。
名詞解釋：
CR：Carriage Return，對應ASCII中轉義字符\r，表示回車；
LF：Linefeed，對應ASCII中轉義字符\n，表示換行；
CRLF：Carriage Return & Linefeed，\r\n，表示回車并換行；
有興趣的，可以看看下表的詳細展示……
| 十進制 | 二進制 | 十六進制 | 字符/縮寫 | 解釋 |
| 0 | 0 | 0 | NUL (NULL) | 空字符 |
| 1 | 1 | 1 | SOH (Start Of Headling) | 標題開始 |
| 2 | 10 | 2 | STX (Start Of Text) | 正文開始 |
| 3 | 11 | 3 | ETX (End Of Text) | 正文結束 |
| 4 | 100 | 4 | EOT (End Of Transmission) | 傳輸結束 |
| 5 | 101 | 5 | ENQ (Enquiry) | 請求 |
| 6 | 110 | 6 | ACK (Acknowledge) | 回應/響應/收到通知 |
| 7 | 111 | 7 | BEL (Bell) | 響鈴 |
| 8 | 1000 | 8 | BS (Backspace) | 退格 |
| 9 | 1001 | 9 | HT (Horizontal Tab) | 水平制表符 |
| 10 | 1010 | 0A | LF/NL(Line Feed/New Line) | 換行鍵 |
| 11 | 1011 | 0B | VT (Vertical Tab) | 垂直制表符 |
| 12 | 1100 | 0C | FF/NP (Form Feed/New Page) | 換頁鍵 |
| 13 | 1101 | 0D | CR (Carriage Return) | 回車鍵 |
| 14 | 1110 | 0E | SO (Shift Out) | 不用切換 |
| 15 | 1111 | 0F | SI (Shift In) | 啟用切換 |
| 16 | 10000 | 10 | DLE (Data Link Escape) | 數據鏈路轉義 |
| 17 | 10001 | 11 | DC1/XON (Device Control 1/Transmission On) | 設備控制1/傳輸開始 |
| 18 | 10010 | 12 | DC2 (Device Control 2) | 設備控制2 |
| 19 | 10011 | 13 | DC3/XOFF(Device Control 3/Transmission Off) | 設備控制3/傳輸中斷 |
| 20 | 10100 | 14 | DC4 (Device Control 4) | 設備控制4 |
| 21 | 10101 | 15 | NAK (Negative Acknowledge) | 無響應/非正常響應/拒絕接收 |
| 22 | 10110 | 16 | SYN (Synchronous Idle) | 同步空閑 |
| 23 | 10111 | 17 | ETB (End of Transmission Block) | 傳輸塊結束/塊傳輸終止 |
| 24 | 11000 | 18 | CAN (Cancel) | 取消 |
| 25 | 11001 | 19 | EM (End of Medium) | 已到介質末端/介質存儲已滿/介質中斷 |
| 26 | 11010 | 1A | SUB (Substitute) | 替補/替換 |
| 27 | 11011 | 1B | ESC (Escape) | 逃離/取消 |
| 28 | 11100 | 1C | FS (File Separator) | 文件分割符 |
| 29 | 11101 | 1D | GS (Group Separator) | 組分隔符/分組符 |
| 30 | 11110 | 1E | RS (Record Separator) | 記錄分離符 |
| 31 | 11111 | 1F | US (Unit Separator) | 單元分隔符 |
| 32 | 100000 | 20 | (Space) | 空格 |
| 33 | 100001 | 21 | ! | exclamation mark |
| 34 | 100010 | 22 | “ | double quote |
| 35 | 100011 | 23 | # | number sign |
| 36 | 100100 | 24 | $ | dollar sign |
| 37 | 100101 | 25 | % | percent |
| 38 | 100110 | 26 | & | ampersand |
| 39 | 100111 | 27 | ‘ | single quote |
| 40 | 101000 | 28 | ( | left/opening parenthsis |
| 41 | 101001 | 29 | ) | right/opening parenthsis |
| 42 | 101010 | 2A | * | asterisk |
| 43 | 101011 | 2B | + | plus |
| 44 | 101100 | 2C | , | comma |
| 45 | 101101 | 2D | – | minus or dash |
| 46 | 101110 | 2E | . | dot |
| 47 | 101111 | 2F | / | forward slash |
| 48 | 110000 | 30 | 0 | |
| 49 | 110001 | 31 | 1 | |
| 50 | 110010 | 32 | 2 | |
| 51 | 110011 | 33 | 3 | |
| 52 | 110100 | 34 | 4 | |
| 53 | 110101 | 35 | 5 | |
| 54 | 110110 | 36 | 6 | |
| 55 | 110111 | 37 | 7 | |
| 56 | 111000 | 38 | 8 | |
| 57 | 111001 | 39 | 9 | |
| 58 | 111010 | 3A | : | |
| 59 | 111011 | 3B | ; | |
| 60 | 111100 | 3C | < | |
| 61 | 111101 | 3D | = | |
| 62 | 111110 | 3E | > | |
| 63 | 111111 | 3F | ? | |
| 64 | 1000000 | 40 | @ | |
| 65 | 1000001 | 41 | A | |
| 66 | 1000010 | 42 | B | |
| 67 | 1000011 | 43 | C | |
| 68 | 1000100 | 44 | D | |
| 69 | 1000101 | 45 | E | |
| 70 | 1000110 | 46 | F | |
| 71 | 1000111 | 47 | G | |
| 72 | 1001000 | 48 | H | |
| 73 | 1001001 | 49 | I | |
| 74 | 1001010 | 4A | J | |
| 75 | 1001011 | 4B | K | |
| 76 | 1001100 | 4C | L | |
| 77 | 1001101 | 4D | M | |
| 78 | 1001110 | 4E | N | |
| 79 | 1001111 | 4F | O | |
| 80 | 1010000 | 50 | P | |
| 81 | 1010001 | 51 | Q | |
| 82 | 1010010 | 52 | R | |
| 83 | 1010011 | 53 | S | |
| 84 | 1010100 | 54 | T | |
| 85 | 1010101 | 55 | U | |
| 86 | 1010110 | 56 | V | |
| 87 | 1010111 | 57 | W | |
| 88 | 1011000 | 58 | X | |
| 89 | 1011001 | 59 | Y | |
| 90 | 1011010 | 5A | Z | |
| 91 | 1011011 | 5B | [ | left/opening bracket |
| 92 | 1011100 | 5C | \ | back slash |
| 93 | 1011101 | 5D | ] | right/closing bracket |
| 94 | 1011110 | 5E | ^ | caret/circumflex |
| 95 | 1011111 | 5F | _ | underscore |
| 96 | 1100000 | 60 | ` | |
| 97 | 1100001 | 61 | a | |
| 98 | 1100010 | 62 | b | |
| 99 | 1100011 | 63 | c | |
| 100 | 1100100 | 64 | d | |
| 101 | 1100101 | 65 | e | |
| 102 | 1100110 | 66 | f | |
| 103 | 1100111 | 67 | g | |
| 104 | 1101000 | 68 | h | |
| 105 | 1101001 | 69 | i | |
| 106 | 1101010 | 6A | j | |
| 107 | 1101011 | 6B | k | |
| 108 | 1101100 | 6C | l | |
| 109 | 1101101 | 6D | m | |
| 110 | 1101110 | 6E | n | |
| 111 | 1101111 | 6F | o | |
| 112 | 1110000 | 70 | p | |
| 113 | 1110001 | 71 | q | |
| 114 | 1110010 | 72 | r | |
| 115 | 1110011 | 73 | s | |
| 116 | 1110100 | 74 | t | |
| 117 | 1110101 | 75 | u | |
| 118 | 1110110 | 76 | v | |
| 119 | 1110111 | 77 | w | |
| 120 | 1111000 | 78 | x | |
| 121 | 1111001 | 79 | y | |
| 122 | 1111010 | 7A | z | |
| 123 | 1111011 | 7B | { | left/opening brace |
| 124 | 1111100 | 7C | | | vertical bar |
| 125 | 1111101 | 7D | } | right/closing brace |
| 126 | 1111110 | 7E | ~ | tilde |
| 127 | 1111111 | 7F | DEL (Delete) | 刪除 |