Intel 8080 Assembler

The following text is an exert from the Assembly language article.

In computer programming, assembly language (or assembler language), sometimes abbreviated asm, is any low-level programming language in which there is a very strong correspondence between the instructions in the language and the architecture's machine code instructions. Assembly language usually has one statement per machine instruction (1:1), but constants, comments, assembler directives, and symbolic labels of, e.g., memory locations, registers, and macros are generally also supported.

Intel 8080 Assembly Language Programming Manual¶

Refer to the Intel 8080 Assembly Language Programming Manual for more about the language and its implementation.

Intel 8080 Assembly Language Symbol Length Limitation

The biggest gotcha is that all identifiers/symbols are unique to 6 characters. For example, the following two variables are treated as the same symbol:

VARIAB1: DB 0
VARIAB2: DB 0

Both are treated as VARIAB. So, be careful when naming variables, functions, and other symbols as you get no assembler warnings or errors and your application will behave unexpectedly.

Assemble assembly applications¶

The CP/M disk image includes two demo assembly applications, DEMO.ASM and SLEEP.ASM. Follow these steps to edit, assemble, and load the demo file:

The DEMO.ASM example¶

List the DEMO.ASM file

type sleep.asm

        ORG     0100H           ; CP/M base of TPA (transient program area)
        OUT     30
        MVI     C,09H           ; Print string function
        LXI     D,MESSAGE       ; Point
        CALL    0005H           ; Call bdos
        RET                     ; To cp/m
MESSAGE:DB      0DH,0AH,'Hello, World!',0DH,0AH,'$'
        END

Assemble the DEMO.ASM file:
```
asm demo
```
Load and link the assembled code:
```
load demo
```
Run the demo application:
```
demo
```

Edit a file with Word-Master¶

in the following steps use the Word-Master text editor to edit a file. It's highly recommended to edit files with Visual Studio Code and then copy the file to the Altair filesystem using the CP/M gf command.

Edit the DEMO.ASM file with Word-Master:
```
wm demo.asm
```
Switch the web terminal to character input mode by selecting Ctrl+L.
Edit the demo.asm file. For example, change Hello, World! text to your name.
Save your updates to the demo.asm file:
1. Select the Esc key.
2. Select E to exit. Your file changes are saved to disk.
Switch the web terminal to line input mode by selecting Ctrl+L.
Then assemble, load, and run the updated demo.asm application.

Sleep assembly example¶

The SLEEP.ASM example uses Intel 8080 input and output port instructions. The SLEEP.ASM application sets a sleep period of 2 seconds using output port 30, waits on input port 30 for the delay period to expire, and then publishes weather data to Azure IoT Central. For more information about Intel 8080 IO port mappings, refer to Intel 8080 input and output ports.

List the SLEEP.ASM file

type sleep.asm

      ORG 0100H   ;CP/M base of TPA (transient program area)
      MVI C,09H   ;Print string function
      LXI D,MSG   ;Point to waiting message
      CALL 0005H  ;Call bdos
      MVI A,2     ;Move 2 to the accumulator to set a 2 second delay
      OUT 30      ;Start timer
LOOP: IN 30       ;Get delay timer state into the accumulator
      CPI 00H     ;If accumulator equal to 0 then timer has expired
      JZ BACK     ;Jump on zero
      JMP LOOP
BACK: MVI C,09H   ;Print string function
      LXI D,PUB   ;Point to publish message
      CALL 0005H  ;Call bdos
      MVI A,0H    ;Move zero to the accumulator
      OUT 32      ;Publish to Azure IoT Central
      MVI C,09H   ;Print string function
      LXI D,FINI  ;Point to Finished message
      CALL 0005H  ;Call Bdos
      RET
MSG:  DB 'Sleeping 2 seconds$'
FINI: DB 0DH,0AH,'Finished$'
PUB:  DB 0DH,0AH,'Publishing to Azure IoT Central$' 
      END

Assemble the SLEEP.ASM file:
```
asm sleep
```
Load and link the assembled code:
```
load sleep
```
Run the demo application:
```
sleep
```