Overview of assembler language structure

Figure 3. Overview of assembler language structure
                                              *-------------------------*
                                              |                         |
                                              |    Source module        |
                                              |    made up of           |
                                              |    source statements    |
                                              |                         |
                                              *------------*------------*
                                                           |
                                                           V Which can be
                                                           |
                                                    EITHER | OR
                              *--------------------------<-*->--------------------------*
                              V                                                         V
                 *------------*------------*                               *------------*------------*
                 |                         |                               |                         |
                 |       INSTRUCTION       |                               |       COMMENT           |
                 |       STATEMENTS        |                               |       STATEMENTS        |
                 |                         |                               |                         |
                 *------------*------------*                               *------------*------------*
                              |                                                         |
                              V Which are of                                            |
                              | three main types                                        |
        *---------------------+---------------------*                                   |
        V                     V                     V                                   |
*-------*-------*     *-------*-------*     *-------*-------*                           |
|  MACHINE      |     |  ASSEMBLER    |     |  MACRO        |                           |
|  Instructions |     |  Instructions |     |  Instructions |                           |
*-------*-------*     *-------*-------*     *-------*-------*                           |
        V                     V                     V                                   |
        *---------------------+---------------------*                                   |
                              |                                                         |
                              V Which are composed of                                   |
                              | from one to four fields                                 |
        *---------------------+---------------------*---------------------*             |
        V                     V                     V                     V             |
*-------*-------*     *-------*-------*     *-------*-------*     *-------*-------*     |
|     NAME      |     |   OPERATION   |     |    OPERAND    |     |    REMARKS    |     |
*-------*-------*     *-------*-------*     *-------*-------*     *-------*-------*     V
        V                     V                     |                     V             |
*-------*-------*     *-------*-------*             |                     *----------->-*
|    No DBCS    |     |    No DBCS    |             V Which, for machine                |
*---------------*     *---------------*             | instructions, is                  |
                                                    | composed of                       |
                                            *-------*-------*                           |
                                            |  EXPRESSIONS  |                           |
                                            *-------*-------*                           |
                                                    |                                   |
                                                    V Which are                         |
                                                    | composed of                       |
                                         *----------*----------*                        V Which are
                                         V                     V                        | composed of
                                 *-------*-------*     *-------*-------*        *-------*-------*
                                 |     TERMS     |     |  Combination  |        |      Any      |
                                 |               |     |  of terms     |        |  Characters   |
                                 *-------*-------*     *-------*-------*        *-------*-------*
                                         V                     V                        V
                                         *---------------------+------------------------*
                                                               |
                                                               V Which are
                                                               | composed of
                                                     *---------*---------*
                                                     |  EBCDIC and DBCS  |
                                                     |  CHARACTERS       |
                                                     *-------------------*

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