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PLC

PLC stands for “Programmable Logic Controller”.

PLC controller can load and run small binary programs (PLC procedures). PLC procedure should be written in a simplified C-like language, compiled and stored in PLC controller memory to be ready to run. myCNC software includes PLC Builder - tiny IDE (Integrated Development Environment) to create and modify PLC procedure source files, compile them to binary code and upload it as RomFS iso image disk to PLC controller memory.

myCNC control has 2 types of built-in PLC systems that named Hardware PLC and Software PLC.

Note that hardware PLC can be launched from software PLC if necessary, through the use of gvarset(100040,HARDWAREPLC); command (replace HARDWAREPLC with your M-command of choice). You can read more on the process in the Software PLC section down below.

Hardware PLC

“Hardware PLC” means PLC system runs inside the CNC control board and able to access directly to CNC controller peripherals (inputs, outputs, PWMs, DACs, ADCs etc). PLC has also API to access to Motion Controller of a myCNC control board, so positioning commands are possible from Hardware PLC.

Hardware PLC is a tiny virtual machine that runs pre-compiled PLC procedures. PLC procedure can be started from

  • G-code program M-code
  • On-screen button
  • Input Pin
  • From TCP Ethernet Socket through Server API

Hardware PLC loop cycle time is 1ms. PLC core runs PLC procedure until the end of next loop. At the end of each loop PLC sleeps for 1ms, then continue running PLC. N-times repeat loop (even empty) will be executed N milliseconds. For example, delay for 10ms can be programmes as

timer=10; do{timer--;}while(timer>0);
IMPORTANT.
Hardware PLC is single-tasking. Only one PLC process can be executed at the moment. 
If new PLC procedure loaded, previous PLC process will be terminated immediately 
and replaced by the new one.

PLC Language

  • PLC operates with 32 bits integer values only. Floating point operations don't work in PLC (typically need to use coefficient conversions to allow for more granular control).
  • There is no need to declare variables. There is very limited space of 32 elements for variables.
  • There a number of pre-defined variables in the PLC
    • eparam - External Parameter variable. A short manual is available here: Eparam
    • proc - variable is used to identify a process running in the PLC.
      The value is sent to the CNC control software and can be used to display Current PLC state (like Idle, Ignition (for plasma cutting), preheat (gas cutting), Tool change, Probing etc)
      • The proc variable can impact many behaviours of the myCNC software, such as jogging speed (using the User Settings value for when the proc is Idle, and using the cutting speed for Plasma and Cutting states).
    • timer - value can be used as time counter inside PLC procedure
    • vexit - variable contains additional exit code. In case of error CNC control software can display Error message depends on vexit exit code.
    • message. The message variable is handled every loop delay time. If message value is not “0” PLC controller sends to CNC control software message code and reset the variable to “0”.
    • pwm01 - variable mapped to PWM #0 register. Writing to this variable will change PWM #0 value.
    • pwm02 - variable mapped to PWM #1 register. Writing to this variable will change PWM #1 value.
    • pwm03 - variable mapped to PWM #2 register. Writing to this variable will change PWM #2 value.
    • pwm04 - variable mapped to PWM #3 register. Writing to this variable will change PWM #3 value.
    • dac01 - variable mapped to DAC #0 register. Writing to this variable will change DAC #0 value.
    • dac02 - variable mapped to DAC #1 register. Writing to this variable will change DAC #1 value.
    • adc01 - variable mapped to ADC #0 register. Reading this variable will return ADC #0 value.
    • adc02 - variable mapped to ADC #1 register. Reading this variable will return ADC #1 value. Variables adc01, adc02 are a bit obsolete. It's better to use gvarget, gvarset functions and The hardware access registers to access to the control board peripherals.

For example, changing the value of PWM01 can be done using the following PLC procedure:

main()
{
   val=eparam;
   if (val>0xfff) {val=0xfff;};
   if (val<0) {val=0;};
   pwm01=val;
   exit(99);	//normal exit
};
PLC is a tiny virtual machine with a very limited register and memory space. 
PLC was created for very simple Inputs/Outputs manipulation. 
Heavy algorithms cannot be handled by PLC.
Please keep in mind this while creating Hardware PLC procedure.
  • PLC operators
Operator Description Example
+
sum
c=a+200;
-
subtract
c=a-150;
*
multiply
c=a*b;
/
divide
c=b/7;
&
logical AND
c=a&7;
|
logical OR
c=b|1;
>>
binary right shift
c=a>>16;
<<
binary left shift
c=1<<n;
==
equal to
if (a==20) ......
!=
not equal to
if (a!=0) ......
>
more than
if (b>0) ......
>=
more or equal than
if (a>=0xf) ......
<
less than
if (c<10) ......
<=
less or equal than
if (a<=b) ......
++
variable post increment
x++;
--
variable post decrement
a--;
  • PLC functions
    • g0moveA - send positioning command for PLC to the Motion controller.
    • portset - set to “1” selected output pin
    • portclear - clear to “0” selected output pin
    • portget - return selected input pin state (“0”, “1”)
    • gvarget - return Global Variable Register value. This function sends an inquiry about Global variable value to myCNC control software running on Host PC and waits till reply received. Waiting time can be 20…200ms depends on Host PC Operating System (Windows, Linux).
    • gvarset - set Global Variable Register to given value. This function sends to myCNC control software inquiry to change Global Variable Register to given value. There is a number of “Mapped” register addresses besides of “real” Global Array registers. List of Mapped addresses is shown in a table below.
Address Description
20000…20100 Print variable value in myCNC control message widget for debugging purpose. Values written to this registers will be printed in myCNC control software in Message widget - this is useful to see values of certain variables directly in the log window as the program is running.

It is possible to access the state of the output via gvarget commands from within the PLC process:

a=gvarget(0x400); //OUT0
b=gvarget(0x407); //OUT7

Starting from 0x400 to represent OUT0, this is a hexadecimal system that is simple to convert to dotted decimals (through the likes of a simple reference site here). Thus, for example, gvarget(0x40d); will return the state of Output #13.

The hardware access registers

Name Address Description
GVAR_HW_INPUTS0 7180
GVAR_HW_INPUTS1 7181
GVAR_HW_INPUTS2 7182
GVAR_HW_INPUTS3 7183
GVAR_HW_OUTPUTS0 7184 YouTube tutorial
GVAR_HW_OUTPUTS1 7185
GVAR_HW_OUTPUTS2 7186
GVAR_HW_OUTPUTS3 7187
GVAR_HW_INPUTS4 7188
GVAR_HW_INPUTS5 7189
GVAR_HW_INPUTS6 7190
GVAR_HW_INPUTS7 7191
GVAR_HW_OUTPUTS4 7192
GVAR_HW_OUTPUTS5 7193
GVAR_HW_OUTPUTS6 7194
GVAR_HW_OUTPUTS7 7195
GVAR_HW_ADC0 7196
GVAR_HW_ADC1 7197
GVAR_HW_ADC2 7198
GVAR_HW_ADC3 7199
GVAR_HW_ADC4 7200
GVAR_HW_ADC5 7201
GVAR_HW_ADC6 7202
GVAR_HW_ADC7 7203
GVAR_HW_DAC0 7270
GVAR_HW_DAC1 7271
GVAR_HW_DAC2 7272
GVAR_HW_DAC3 7273
GVAR_HW_DAC4 7274
GVAR_HW_DAC5 7275
GVAR_HW_DAC6 7276
GVAR_HW_DAC7 7277
GVAR_HW_PWM0 7278
GVAR_HW_PWM1 7279
GVAR_HW_PWM2 7280
GVAR_HW_PWM3 7281
GVAR_HW_PWM4 7282
GVAR_HW_PWM5 7283
GVAR_HW_PWM6 7284
GVAR_HW_PWM7 7285

Software PLC

“Software PLC” means PLC system runs inside the myCNC software and controls CNC controllers peripherals through Software API.

The main advantage of Software PLC is multitasking. All PLC procedures are running simultaneously and independent from each other.

Software PLC cycle time is 100ms, so Software PLC is suitable for wide range of slow applications like automatic lubricant control, fume exhaust control, alarm sensors control etc.

  • All Software PLC procedures (except “system” procedures) are compiled and started simultaneously in separate threads with myCNC software start or after “Build All” button pressed in PLC Builder/Software PLC.
  • “System” PLC procedures are procedures with names start with
    __ (double underscore)

    symbols. “System” procedures are not started automatically with the myCNC software start, but instead can be started automatically with some events or manually. There are a few pre-defined “System” PLC handlers-

Handler Name Comments
__HANDLER_INIT
The procedure executed just after myCNC software started AND configuration is sent to the myCNC control board. The procedure can be used to perform some inputs testing and switch outputs just after the software started.
__HANDLER_EXIT
The procedure executed just before the myCNC software closed.
__HANDLER_GCODE_START
The procedure executed just before the myCNC software run g-code (after pressing PLAY button)
__HANDLER_GCODE_STOP
The procedure executed just after the myCNC software finished g-code running (after pressing STOP/PAUSE button)
__BV17
Initially named BV17, this Software PLC had double underscores added to remove an issue with automatic enabling of the testing mode for the controller peripherals (by becoming a System PLC, it prevents the procedure from starting automatically when the program is loaded).

Variables used in Software PLC:

VariableUseExampleComment
100020 Jog the selected axis (100020 through to 100027) gvarset(100020, 100); Negative values are not accepted, use 0-X (for example, gvarset(100020, 0-100);)
100040 Launch a Hardware PLC from within a Software PLC gvarset(100040, 607); This will launch Hardware PLC M607
100041 Eparameter to feed into the Hardware PLC being launched using 100040 gvarset(100041, 333); Used before gvarset(100040, 607);, this will set eparam=333

Compare Software and hardware PLC

Parameter Software PLC Hardware PLC
Loop time 100ms 1ms
Hardware access Slow, through the software and Ethernet communication Fast, direct in myCNC controller
Multitasking Yes, all PLC procedures are running simultaneously in separate threads No, starting new procedure will terminate a current procedure
Code size for PLC procedure 16k bytes 512 bytes
Total disk size for PLC procedures Unlimited 8k bytes

Language Core for Software and Hardware PLC are almost the same so language syntax is pretty the same and similar to C-language but VERY VERY stripped down.

PLC Language

PLC variables

  • “32” - is a total number of variables PLC supports
  • No need to define variables in source text. Variable name reserved when fist used. For example in line
    output0=15;

    PLC builder will define variable “output0” and assign the value to “15”

PLC predefined variables

  • var00var15 : This variables are initialised before PLC procedure start from values defined in plc-variables.xml file.
  • proc : proc variable value can be displayed on myCNC screen with display name “display-plc-proc” and can be used to show current status of PLC procedure
  • message : If message value set to non-zero value, PLC controller will send a message to myCNC Control Core or myCNC software with parameters defined in variables
    message,
    var00 (usually defined as command as well) and
    var01 (defined as parameter).
    This way PLC controller able to communicate with Motion Controller and Host Software. Message variable is handled and cleared by PLC controller while “loop” operation, so message variable assign usually followed by short timeout loop like
    timer=2;do{timer--;}while(timer>0);

    Examples:

    //send to myCNC software information spindle speed is "0"
    command=PLC_MESSAGE_SPINDLE_SPEED_CHANGED;
    parameter=0;
    message=PLCCMD_REPLY_TO_MYCNC;
    timer=2;do{timer++;}while (timer>0);
    //Probing for Plasma Cutting.
    g0moveA(0x0,0x4,0-30000);                  //Start move down
    do { code=gvarget(6060); }while(code!=0);  //Wait till Motion Controller confirm moving started
    do{
     code=gvarget(6060);               //check Motion Controller (MC) current status
     sens=portget(INPUT_IHC);          //and check Probe input 
     if (sens==0)
     {
       message=PLCCMD_LINE_STOP;       //Send to MC command to Stop current line and wait next command
       code=1;                         //Set flag to exit from the loop
     };
    }while (code==0);                  //Exit from loop is motion finished OR Probe sensor pressed 

PLC defines

Name Value Comment
PLCCMD_MOTION_CONTINUE 1001
PLCCMD_MOTION_SKIP 1002
PLCCMD_MOTION_SOFT_SKIP 1003
PLCCMD_MOTION_PAUSE 1004
PLCCMD_PLC_PAUSE 1005
PLCCMD_PLC_FORK_PAUSE 1006
PLCCMD_LINE_SOFT_STOP 1007
PLCCMD_LINE_STOP 1008
PLCCMD_REPLY_TO_MYCNC 1100
PLCCMD_SET_CNC_VAR 1010
PLCCMD_SET_THC_VAR 1011
PLCCMD_SET_DEVICE_VAR16 1012
PLCCMD_SET_DEVICE_VAR32 1014
PLCCMD_SET_CNC_EXTVAR 1020
PLCCMD_MOTION_ABORT 1032
PLCCMD_MOTION_BREAK 1033
PLCCMD_SAVE_POS 1040
PLCCMD_THC_START 1050
PLCCMD_THC_STOP 1051
PLCCMD_THC_PAUSE 1052
PLCCMD_THC_CONTINUE 1053
PLCCMD_WATCHBIT1_ON 1060
PLCCMD_WATCHBIT2_ON 1061
PLCCMD_WATCHBIT3_ON 1062
PLCCMD_WATCHBIT4_ON 1063
PLCCMD_TRIGGER1_ON 1060
PLCCMD_TRIGGER2_ON 1061
PLCCMD_TRIGGER3_ON 1062
PLCCMD_TRIGGER4_ON 1063
PLCCMD_TRIGGER1_OFF 1064
PLCCMD_TRIGGER2_OFF 1065
PLCCMD_TRIGGER3_OFF 1066
PLCCMD_TRIGGER4_OFF 1067
PLCCMD_WATCHBIT1_OFF 1064
PLCCMD_WATCHBIT2_OFF 1065
PLCCMD_WATCHBIT3_OFF 1066
PLCCMD_WATCHBIT4_OFF 1067
PLCCMD_WATCHBIT5_ON 1068
PLCCMD_WATCHBIT6_ON 1069
PLCCMD_WATCHBIT7_ON 1070
PLCCMD_WATCHBIT8_ON 1071
PLCCMD_WATCHBIT5_OFF 1072
PLCCMD_WATCHBIT6_OFF 1073
PLCCMD_WATCHBIT7_OFF 1074
PLCCMD_WATCHBIT8_OFF 1075
PLCCMD_WAIT_FOR_CAMERA 1090
PLCCMD_WAIT_VARSET 1091
PLCCMD_WAIT_VARCLEAR 1092
PLCCMD_CAMERA_START 1093
PLCCMD_CAMERA_FINISH 1094
PLCCMD_PLC_DEBUG 1098
PLCCMD_PLC_RESTART 1099
PLC_BROADCAST_INQUIRY0 1200
PLC_BROADCAST_INQUIRY1 1201
PLC_BROADCAST_INQUIRY2 1202
PLC_BROADCAST_INQUIRY3 1203
PLC_BROADCAST_INQUIRY4 1204
PLC_BROADCAST_INQUIRY5 1205
PLC_BROADCAST_INQUIRY6 1206
PLC_BROADCAST_INQUIRY7 1207
PLC_BROADCAST_INQUIRY8 1208
PLC_BROADCAST_INQUIRY9 1209
PLC_BROADCAST_INQUIRY10 1210
PLC_BROADCAST_INQUIRY11 1211
PLC_BROADCAST_INQUIRY12 1212
PLC_BROADCAST_INQUIRY13 1213
PLC_BROADCAST_INQUIRY14 1214
PLC_BROADCAST_INQUIRY15 1215
PLC_BROADCAST_OK 1220
PLC_BROADCAST_ABORTED 1221
PLCCMD_MODBUS_SPINDLE_SPEED 1230
PLCCMD_MODBUS_SPINDLE_CMD 1231
PLCCMD_SET_PIDTIME 1240
Note on PLC define naming

Please note that there exist some limitations of the preprocessor that parses the #define lines. Specifically, it is not possible to have a full name of one parameter be part of the name of another parameter.

For example, an argument name such as OUTPUT_SPINDLE (present by default in the pins.h file), means that there must be no other define-names containing this substring. As such, names such as

OUTPUT_SPINDLE_COOL
OUTPUT_SPINDLE_BEARING
OUTPUT_SPINDLE_CONE

are NOT allowed, ssince they all contain the string “OUTPUT_SPINDLE”. Instead, you can make argument names such as

OUTPUT_BEARING_SPINDLE

or

OUTPUT_CONE_SPINDLE

since those do not contain the exact string from before. Failure to properly define your arguments in such a manner and then utilizing them in your PLC commands will result in a error during compilation with a label “syntax error, unexpected ID”.

PLCCMD_MOTION_CONTINUE and PLCCMD_MOTION_SKIP

The abovementioned PLCCMD_MOTION_CONTINUE and PLCCMD_MOTION_SKIP commands are highly useful for certain applications since typically the motion controller runs commands one by one. By design, if within a running program the next code is a PLC M-code, then the movement will be stopped and the controller will run the PLC program. A message from within the PLC called PLCCMD_MOTION_CONTINUE is used to instruct the Motion controller to read and run the next code from the buffer (thus starting the next motion command).

After this code, the PLC procedure continues running through its code while at the same time the next motion code is launched. In this way, both the PLC procedure and the motion command will be running simultaneously.

This is useful for applications such as homing since it makes it possible to both move the axis and monitor the home sensor in the PLC procedure at the same time. That way when the sensor is activated, the current movement command will need to be stopped. A different message called PLCCMD_MOTION_SKIP is then used - the motion controller will cancel current motion (it will stop moving) and will read the next code from the buffer.

PLC processes named

PLC process name Value Comment
plc_proc_check_plasma 10
plc_proc_venting 11
plc_proc_start_power 12
plc_proc_cooling 14
plc_proc_plasma 15
plc_proc_wait_plasma 18
plc_proc_pierce 27
plc_proc_no_plasma 62
plc_proc_check_preflow 16
plc_proc_check_cutflow 17
plc_proc_check_gases 23
plc_proc_test_out 24
proc_m_function 30
proc_zeroing 32
plc_proc_probing 33
plc_proc_ignition 50
plc_proc_preheat 51
plc_proc_soft_start 52
plc_proc_piercing 53
plc_proc_flame 54
plc_proc_cutting 60
plc_proc_purge 61
plc_proc_no_cutting 62
plc_proc_moveup 65
plc_proc_spindle 70
plc_proc_idle 0

PLC exit codes list.

Normally PLC procedure should return code 99.

exit(99);

In case Error happened PLC procedure may return an error code. MyCNC software will catch exit code and report about Error if the error code is in PLC exit codes list.

Exit code name Value Comment
plc_process 0 exit code is zero when PLC process is not finished yet
plc_exit_gas_fail 2 PLC aborted, No air pressure sensor
plc_exit_plasma_timeout 3 PLC aborted, No Arc sensor signal Timeout
plc_exit_plasma_fail 4 PLC aborted, PLC Plasma Start cutting procedure error
plc_exit_alarm_key 5 PLC aborted, Emergency key pressed
plc_exit_coolant_fail 6 PLC aborted, No Coolant flow sensor
plc_exit_probe_error 7 PLC aborted, No signal from probe sensor
plc_exit_motor_shorted 8 PLC aborted, Motor short circuit detected (ET2/ET4 boards)
plc_exit_broadcast_error 10 Error send broadcast message in multi-device configuration
plc_exit_normal 99 Normal exit
plc_exit_extern_break 100 PLC procedure aborted from outside of PLC core

PLC messages

Message name Value Comment
PLC_MESSAGE_PLASMA_OK 101
PLC_MESSAGE_WATCHBIT_ACTION 110
PLC_MESSAGE_SPINDLE_SPEED_CHANGED 120
PLC_MESSAGE_PULL_OUT_TOOL 130
PLC_MESSAGE_SPINDLE_TURNING 131
PLC_MESSAGE_ENCODER_DATA 140
PLC_MESSAGE_GVAR_VALUE 141
PLC_MESSAGE_UID 142
PLC_MESSAGE_HCONTROL_OFFSET 144
PLC_MESSAGE_TANGENT_ANGLE 145
PLC_MESSAGE_USER 146
PLC_MESSAGE_HCONTROL_JSPEED 147
PLC_MESSAGE_HCONTROL_DC 148
PLC_MESSAGE_ASK_RECALC 150
PLC_MESSAGE_SOFTLIMIT_STOP 151
PLC_MESSAGE_GVARSET 153
PLC_MESSAGE_IHC_NOT_CONNECTED 155
PLC_MESSAGE_IHC_ERROR 156
PLC_MESSAGE_LATHE_GEARS 160
PLC_MESSAGE_ERR_VM -1
PLC_MESSAGE_ERR_ROMFS -2
PLC_MESSAGE_MOTION_BUFFER_EMPTY -5
PLC_MESSAGE_ERR_SENSOR_COOLANT -10
PLC_MESSAGE_ERR_SENSOR_AIR -11
PLC_MESSAGE_ERR_SENSOR_GAS -12
PLC_MESSAGE_ERR_SENSOR_OXYGEN -13
PLC_MESSAGE_ERR_SENSOR_PLASMA -14
PLC_MESSAGE_ERR_PROBING -15
PLC_MESSAGE_ERR_PLASMA_FAIL -20
PLC_MESSAGE_ERR_PLASMA_TIMEOUT -21
PLC_MESSAGE_PRESSED_ALARM_KEY -30
PLC_MESSAGE_PRESSED_STOP_KEY -31
PLC_MESSAGE_MOTOR_SHORTED -35
MAPPED_OUT_THC_LOWSPEED 63
MAPPED_OUT_LOW_MOTOR_CURRRENT 65

Controller peripherals API from PLC procedures

A number of Global variable addresses are mapped to Hardware Inputs/Outputs. PLC procedure can access the controller peripherals through GVarGet/GVarSet function. Addresses to access to controller hardware are listed below

Variabe Name Address Description
GVAR_HW_INPUTS0…
GVAR_HW_INPUTS3
7180…
7183
GVAR_HW_OUTPUTS0…
GVAR_HW_OUTPUTS3
7184…
7187
GVAR_HW_INPUTS4…
GVAR_HW_INPUTS7
7188…
7191
GVAR_HW_OUTPUTS4…
GVAR_HW_OUTPUTS7
7192…
7195
GVAR_HW_ADC0…
GVAR_HW_ADC7
7196…
7203
GVAR_HW_DAC0…
GVAR_HW_DAC7
7270…
7277
GVAR_HW_PWM0…
GVAR_HW_PWM7
7270…
7277
GVAR_ET5_ENCODER …
GVAR_ET5_ENCODER_Z …
GVAR_ET5_ENCODER_WZ …
GVAR_ET5_ENCODER …
GVAR_MODBUS_READ
GVAR_THC0_CONTROL 7570
GVAR_THC1_CONTROL 7575
GVAR_CURRENT_MOTION_CODE 6060
GVAR_MD_MASTER_MOTION_CODE 7140
GVAR_CURRENT_TOOL_NUMBER 5400
GVAR_HCONTROL2_VREF
GVAR_PLC_MOVE_PROCESS
GVAR_CAMERA_READY 7090
GVAR_CURRENT_MACHINE_POSITION 5021, 5022, 5023, 5024, 5025, 5026
GVAR_CURRENT_PROGRAM_POSITION 5041, 5042, 5043, 5044, 5045, 5046
GVAR_ENCODER_Z_EVENT
17001 Return Current PROGRAM X Position in PLC units (0.01mm)
17002 Return Current PROGRAM Y Position in PLC units (0.01mm)
17003 Return Current PROGRAM Z Position in PLC units (0.01mm)
17004 Return Current PROGRAM A Position in PLC units (0.01degree)
17005 Return Current PROGRAM B Position in PLC units (0.01degree)
17006 Return Current PROGRAM C Position in PLC units (0.01degree)
17007 Return Current PROGRAM U Position in PLC units (0.01mm)
17008 Return Current PROGRAM V Position in PLC units (0.01mm)
17009 Return Current PROGRAM W Position in PLC units (0.01mm)
17021 Return Current MACHINE X Position in PLC units (0.01mm)
17022 Return Current MACHINE Y Position in PLC units (0.01mm)
17023 Return Current MACHINE Z Position in PLC units (0.01mm)
17024 Return Current MACHINE A Position in PLC units (0.01degree)
17025 Return Current MACHINE B Position in PLC units (0.01degree)
17026 Return Current MACHINE C Position in PLC units (0.01degree)
17027 Return Current MACHINE U Position in PLC units (0.01mm)
17028 Return Current MACHINE V Position in PLC units (0.01mm)
17029 Return Current MACHINE W Position in PLC units (0.01mm)

Launching a PLC command using an on-screen button

The following video illustrates the process of creating a button to launch a software PLC command (a similar process can also be used for hardware PLCs):

Launching a Hardware PLC procedure from Software PLC

It is possible to launch Hardware PLC procedures from within a Software PLC command. This can be done for purposes such as utilizing certain commands are not available from the Software PLC, and that some require low-latency sensor monitoring. It also has the added benefit of utilizing the unlimited number of procedures that can work simultaneously in Software PLC, allowing the user create things such as permanent while loops, etc.

For example, a code such as:

main()
{
 
gvarset(100040,602);
 
exit(99);
 
};

will launch Hardware PLC M602 from the specified Software PLC.

Additionally, the Param variable can also be used to call a Hardware PLC with a certain eparam variable.

For example, adding a line such as

gvarset(100041, Param);

will launch the M602 Hardware PLC with the Param variable.

Jog from PLC

NOTE: Jog from PLC requires a firmware update. As of February 2022, the feature is available in the Testing firmware branch.

myCNC allows the user to call for a jog command from within PLCs. The advantage of this motion mode is that it allows to perform tasks (such as changing the speed and direction of movement, as well as turning the motion for a particular axis on or off), all without stopping. This is useful in such applications as homing along multiple (for example, three) axes. Such an example (with simultaneous positioning along the X and Y axes) is available here: PLC Examples

In this mode, the acceleration is set via the following command:

gvarset(8631,100); //acceleration time 100ms = 0.1s

while the speed is set via the global variable #8634 (the axis mask is stored in the high-order byte):

gvarset(8634,((1<<24)|1000)); //Jog speed for X
gvarset(8634,((2<<24)|1000)); //Jog speed for Y
gvarset(8634,((4<<24)|1000)); //Jog speed for Z

A sample motion code may therefore look the following way:

jog()                           
{                 
 gvarset(8631,100); //acceleration time 100ms = 0.1s       
 gvarset(5539,1); //switch to fast g0moveA implementation 
 gvarset(8632,1000); //Jog Speed 1m/min 
 gvarset(8634,((1<<24)|1000)); //Jog speed for X            
 gvarset(8634,((2<<24)|1000)); //Jog speed for Y             
 gvarset(8634,((4<<24)|1000)); //Jog speed for Z              
 
 gvarset(8635,1); //Jog X+         
 timer=2000;       
 do       
  { 
     timer--;             
     if ((timer&0xff)==0)  {    gvarset(8635,1);   };
   }while(timer>0);         
 
 gvarset(8634,((1<<24)|500)); //Speed 500 for X 
 gvarset(8635,1); //Jog X+
 timer=2000;    
 do
  { 
     timer--;  
     if ((timer&0xff)==0)  {    gvarset(8635,1);   };                
   }while(timer>0);
 
 gvarset(8634,((1<<24)|200)); //Speed 200 for X       
 gvarset(8635,1); //Jog X+           
 timer=2000; 
 do                       
  {                              
     timer--;  
     if ((timer&0xff)==0)  {    gvarset(8635,1);   };      
   }while(timer>0);                         
 
 gvarset(8635,2+1<<8); //Jog X- AND Y+ Simultaneously  
 timer=2000;                  
 do                                
  {           
     timer--;         
     if ((timer&0xff)==0) 
     {                         
       gvarset(8635,2+1<<8); //Jog X- AND Y+ Simultaneously 
     };                                
   }while(timer>0);                 
 
   gvarset(8635,0);             
   };

The following variables may be used for this jog functionality:

Variable name Variable #
GVAR_G0PLC_SPEED 8630
GVAR_G0PLC_TIME 8631
GVAR_G0PLC_SPEED_UNITS 8632
GVAR_PLC_JOGSPEED_UNITS 8634
GVAR_PLC_JOG 8635

An example of a homing PLC that utilized this functionality is shown below. This PLC is designed for the Z-axis only:

#include pins.h
 
wait_move()
{
    do { code=gvarget(6060); }while(code!=0x4d);  //wait till motion finished
};
 
show_error()
{
    gvarset(9121,1); //bring up popup message 21 - this can be customized
    timer=50;do{timer--;}while(timer>0);
    message=PLCCMD_MOTION_BREAK;	//1033
    exit(99);
};
 
find_home_z()
{
 
  gvarset(5521,1); //disable hardware limits
  gvarset(5525,1); //disable software limits
 
  gvarset(8631,50); //acceleration time 100ms = 0.05s
 
  statez=0; //we set the "triggered" state to 0 by default
  speed=500;
  speed_slow=100; //used on rollback for better precision
 
  direction=(4<<8); //set the direction variable to Z-
 
  gvarset(8634,(4<<24)|speed); //Jog speed for Z
 
  gvarset(8635,direction); //jog in the set direction Z-
  timer=0;
  do
   {
      changed=0;
      if (statez==0) //to home X
       {
          sens=portget(INPUT_HOME_Z); //get state of home x sensor
          if (sens!=0)
          {
            statez=1;
            gvarset(8634,(4<<24)|speed_slow); //Jog speed for Z
            changed=1;
          };
       };
      if (statez==1) //rollback from home Z
       {
          sens=portget(INPUT_HOME_Z); //receive the state of the sensor 
          if (sens==0)
          {
            statez=2; 
            changed=1; 
          };
       };
 
 
  if (changed!=0) //if any of the sensors state is changed
  {
    direction=0; //set direction to 0 (no movement) before flipping
    if (statez==0) { direction=direction | (4<<8);  };  //direction set to X-
    if (statez==1) { direction=direction | 4;  }; //direction set to X+
    gvarset(8635,direction); //jog in new direction for the axes
  };
 
 
 
      if ((timer&0xff)==0)   {     gvarset(8635,direction);    };
      timer++;
      ready=(statez==2);
 
    }while(ready==0);
 
 
   gvarset(8635,0); wait_move(); //stop jog
 
};
 
main()
{
 
  gvarset(8631,50); //acceleration time 50ms = 0.05s
  gvarset(5539,1); //switch to fast g0moveA implementation
 
  find_home_z();
 
 
  exit(99);  //normal exit 
};

The PLC above can be combined with the XY homing (linked at the start of this section) to create simultaneous XYZ homing. In general, the Jog from PLC functionality allows for this simultaneous movement, cutting down on the previously required separate procedures per each axis.

plc/plc.txt · Last modified: 2022/11/07 16:03 by ivan

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