What should be paid attention to when programming and allocating space for PIC microcontrollers?

The control part uses PICl6F7X series microcontrollers, which are programmed in assembly language. The running speed is fast and can meet the system requirements. Most of the control used here is digital signal control, and the motor control has only two states: open and closed. The coordinated actions of the two arms, body, head, feet, etc. are required during the action. The entire control system is relatively complex, so some issues need to be paid attention to in PIC program writing and space allocation.

1. Use of action flags

In the whole control, there are many combined actions. When all the action positioning is controlled by photoelectric switches, there are some problems in programming. For example, if the left hand is required to rise to the applause position and the right hand is required to rise to the hand-raising position (the initial position of the hand is at the lowest lower position), the photoelectric switch 0 is effective (that is, it is blocked when it is 0), and reaches the correct position. With simple understanding, it can be written as the following program:

listP=16c73

calllefthandup

callrighthandup

LOcallreadinsignal

bdsscsl_v,1efthandlIGBTs

calllefthandstop

btfsccsl_v,righthandlight4

gotoL0

callrighthandstop

L1callreadinsignal

btfsccsl_v,lefthandlight3

gotoL1

calllefthandstop

:

Lefthandlight represents the photoelectric switch, which is used to determine whether it has reached the corresponding position. 1 represents the lowest position of the arm; 2 represents the handshake position of the arm; 3 represents the applause position of the arm; 4 represents the high hand-raising position of the arm. The above program describes the process of the left arm rising to the hand-raising position and the right arm rising to the applause position and stopping. First determine whether the left hand has reached it, if it has, the left hand stops, then check whether the right hand has reached the hand-raising position, if it has, stop, otherwise loop the above detection until the left hand reaches the applause position and the right hand reaches the hand-raising position.

Note that 3 and 4 here represent the applause position and the hand-raising position. After the loop detection, the arm can stop at each position, but the mechanical action has inertia, and the mechanical stop position may be a little above or below the position, which affects the following actions. The mechanical action may malfunction after several actions, that is, the program cannot run normally. In this case, it is necessary to modify the program writing method and use the flag bit to control the action. If the control flag bit is used, the flag position must be set to zero in the action sub-function. The program is as follows:

listp=16c73

:

actlonstopflagequOx6e; bit definition

lefthandfla8cqu0x0; 0 means stop the left hand action

rightbandflagequOxl; O means stop the right hand movement

:

MOV lwOx03

MOV Wfactionstopflag

calllefthanduo

callrighthandup

L2callreadinsignal

btfsscsl_v,lefthandhght3

calllefthatldotop

btfsscsl_v,righthandlight4

callrighthandstop

MOV lwOx00

subwfactionstopflag,w

btfssstatus,z

gotoL2

Continue with the following procedure

Activstopflag represents the action flag parameter, which assigns a value to the action flag. The action stop function will clear the flag value. The above program has the same function as the previous program, realizing the action of the two arms. The above program describes whether the left hand reaches the applause position and stops, and whether the right hand reaches the hand-raising position and stops. Check whether the action flag is zero. If not, keep looping and checking; if yes, execute the following program.

2. Different uses of GOTO and CALL instructions

In the PIC assembly program, CALL and GOT0 instructions are used in different occasions. Generally speaking, the CALL instruction is mostly used between the subprogram and the main program; and the GOTO instruction is mostly used between the state transition modules, that is, entering another state from this state without returning. Since the stack of the PIC microcontroller is limited, the GOTO statement cannot be used endlessly in the program, which will cause the stack to overflow and the program cannot run normally. The internal loops of each small program occupy a small number of stack levels, so it is feasible to use the GOTO instruction, but in a large program, using GOTO cannot return to the next instruction of the program before the call. After the CALL instruction completes the call to the subroutine, it returns to the program before the call. The program is as follows:

listD=16c76

start:ca11setcpu

callautomatlsn, statel

L3callreadinsignal

btfsccs2_v,ultrasonicdetectl

gotoL3

gotoautonatlsmstate2

:

automatlsmstate2:

return

auatomaTIsmstate1 and automatismstate2 represent two states, and uhrasonicdetect1 represents an input ultrasonic detection signal. The above program describes calling the automatismmstate1 state, and after execution, the following detection ultrasonicdetect is performed. If there is no trigger, the detection will be looped. If triggered, it will enter the automatismstate2 state, and it will not return to the following program after execution.

3. Different usage of status flags Z and C

When judging the flag, Z (zero flag) and C (borrow flag) are different. When Z is 1, it means the result above is 0, and when Z is 0, the result is not 0. When C is 1, there is a borrow, and when C is 0, there is no borrow. When using a timer, the C flag is generally used. This is because when a certain action is completed to check the timer, the time may not have arrived, or it may be just right, or it may have exceeded the time. As long as the time has arrived or exceeded, the timer must be turned off as required, as described in the following program. If the Z flag is used, it may not be detected when it is equal to 0, and the stop state cannot be determined, while using z can control the timing well. Z is mostly used for general calculations, such as the previous action flag.

listD=16c76

callopentimerO

L4 MOV lwd '30'

subwft0_v2,W

btfssstatus,c

gotoL4

cauclosetimer0

The program checks whether the time reaches 1.5s. If not, it waits in a loop. If it reaches 1.5s or the detection time has passed, it turns off the timer and executes the following program.

In short, using appropriate methods in programming PIC microcontrollers can make the entire program run stably, and the use of program space will be reduced, avoiding bugs in debugging.