8086 assembler tutorial for beginners (part 12)

Controlling External Devices


There are 7 devices attached to the emulator: traffic lights, stepper-motor, LED display, thermometer, printer, robot and simple test device. You can view devices when you click "Virtual Devices" menu of the emulator.

For technical information see I/O ports section of emu8086 reference.

In general, it is possible to use any x86 family CPU to control all kind of devices, the difference maybe in base I/O port number, this can be altered using some tricky electronic equipment. Usually the ".bin" file is written into the Read Only Memory (ROM) chip, the system reads program from that chip, loads it in RAM module and runs the program. This principle is used for many modern devices such as micro-wave ovens and etc...



Traffic Lights



Usually to control the traffic lights an array (table) of values is used. In certain periods of time the value is read from the array and sent to a port. For example:
; controlling external device with 8086 microprocessor. 
; realistic test for c:\emu8086\devices\Traffic_Lights.exe 

   #start=Traffic_Lights.exe#

   name "traffic"


   mov ax, all_red
   out 4, ax


   mov si, offset situation


   next:
   mov ax, [si]
   out 4, ax

   ; wait 5 seconds (5 million microseconds) 
   mov     cx, 4Ch    ;    004C4B40h = 5,000,000 
   mov     dx, 4B40h
   mov     ah, 86h
   int     15h


   add si, 2 ; next situation 
   cmp si, sit_end
   jb  next
   mov si, offset situation
   jmp next

   ;                        FEDC_BA98_7654_3210 
   situation        dw      0000_0011_0000_1100b
   s1               dw      0000_0110_1001_1010b
   s2               dw      0000_1000_0110_0001b
   s3               dw      0000_1000_0110_0001b
   s4               dw      0000_0100_1101_0011b
   sit_end = $


   all_red          equ     0000_0010_0100_1001b




Stepper-Motor



The motor can be half stepped by turning on pair of magnets, followed by a single and so on.

The motor can be full stepped by turning on pair of magnets, followed by another pair of magnets and in the end followed by a single magnet and so on. The best way to make full step is to make two half steps.

Half step is equal to 11.25 degrees.
Full step is equal to 22.5 degrees.

The motor can be turned both clock-wise and counter-clock-wise.

open stepper_motor.asm from c:\emu8086\examples

See also I/O ports section of emu8086 reference.





Robot



Complete list of robot instruction set is given in I/O ports section of emu8086 reference.

To control the robot a complex algorithm should be used to achieve maximum efficiency. The simplest, yet very inefficient, is random moving algorithm, open robot.asm from c:\emu8086\examples

It is also possible to use a data table (just like for Traffic Lights), this can be good if robot always works in the same surroundings.





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