===== M88, M89 PLC procedures. Stop Motion if Input pin activated =====

Video recap of the manual is available here:

{{youtube>L5-l7CDjIGA?large}}


One of the most popular job for the PLC procedure is moving to given direction till input pin triggered.

It's used in 
  * Homing procedures, 
  * Probing, 
  * Tool Length measure
  * Surface measure
  * Gantry Alignment procedure
  * and many others

This procedure can be handled in Hardware PLC. We offer M88 and M89 PLC procedures which do this job as a standard procedure. However, it can be customized easily according to customer needs.


A source code for M88 PLC procedure is shown below

<code C M88.plc>
main ()
{

  input=eparam&0xFFFF;	//P-parameter
  state=eparam>>16;	//L-parameter

  message=PLCCMD_MOTION_CONTINUE;
  timer=30;do{timer--;}while(timer>0);

  ready=0;

  do {
    a=portget(input);
    if (state==0)
    {
      if (a==0) {ready=1;};
    };
    if (state!=0)
    {
      if (a!=0) {ready=1;};
    };
  }while(ready==0);

  message=PLCCMD_MOTION_SOFT_SKIP;
  timer=30;do{timer--;}while(timer>0);

  exit(99);
};
</code>


Input pin number and pins state (normally opened/closed) comes from G-code P/L parameters in **eparam** internal variable.
Pin number comes in P-parameter and pin state in L-parameter.
  * L=0 means the procedure waits logical "0" on selected input pin
  * L=1 means the procedure waits logical "1" on selected input pin

Example:
<code>M88 P7 L0 (The procedure will wait "0" level on input pin #7)
G90 G0X-1000 F300</code>

<code>M88 P3 L1 (The procedure will wait "1" level on input pin #3)
G90 G0Y300 F100</code>

A two-lines block to decode Input pin number and a pin state from **eparam** variable is shown below
<code C M88.plc>
  input=eparam&0xFFFF;	//P-parameter
  state=eparam>>16;	//L-parameter
</code>


After input pin number and state is decoded, the PLC procedure sends to the Motion controller a command to start next G-code line which is supposed to be a G0-positioning line.

<code C>
  message=PLCCMD_MOTION_CONTINUE;
  timer=30;do{timer--;}while(timer>0);</code>
  
Then the PLC procedure tests selected pin and is waiting till the pin comes to the given state (depends on L/state parameter)  
The test code is wrapped in **do{}while;** loop.

<code C>
  ready=0;

  do {
    a=portget(input);
    if (state==0)
    {
      if (a==0) {ready=1;};
    };
    if (state!=0)
    {
      if (a!=0) {ready=1;};
    };
  }while(ready==0);
</code>


After the pin came to the given state, the PLC sends to the Motion controller to skip the current motion command and load the next. 

<code>
  message=PLCCMD_MOTION_SOFT_SKIP;
  timer=30;do{timer--;}while(timer>0);
</code>

There are 2 scenarios how to Stop the current motion.
  - Immediate STOP (abort pulses generation right away)
  - Soft STOP (do soft deceleration with given deceleration time, programmed as **Soft stop time, s** in Configuration settings of the myCNC control software.

If motion speed is low and you need to find a precise position of input pin triggered you would need **Immediate STOP**. However, if motion speed is high and you need to find the first estimate, Immediate STOP would be harmful for machine mechanics and **Soft STOP** might be more preferable.

The Immediate of Soft stop can be choosen by sending PLC message to the Motion Controller

^ Message Code ^ Value ^ Description ^
| PLCCMD_MOTION_SOFT_SKIP | 1003 | Soft stop and jump to the next command |
| PLCCMD_MOTION_SKIP | 1002 | Immediate stop and kump to the next command | 

M88.plc procedure does **Soft Stop** if a input pin activated.
M89.plc procedure does **Immediate Stop** if a input pin activated.

The only difference between M88 and M89 procedures are message to the Motion controller to skip current motion.

for M89.plc the code is
<code>
  message=PLCCMD_MOTION_SKIP;
  timer=30;do{timer--;}while(timer>0);
</code>

A complete source for M89.plc is shown below

<code C M89.plc>
main ()
{

  input=eparam&0xFFFF;	//P-parameter
  state=eparam>>16;	//L-parameter

  message=PLCCMD_MOTION_CONTINUE;
  timer=30;do{timer--;}while(timer>0);

  ready=0;

  do {
    a=portget(input);
    if (state==0)
    {
      if (a==0) {ready=1;};
    };
    if (state!=0)
    {
      if (a!=0) {ready=1;};
    };
  }while(ready==0);

  message=PLCCMD_MOTION_SKIP;
  timer=30;do{timer--;}while(timer>0);

  exit(99);
};
</code>