VEX programming without transmitter

I am programming the VEX controller in Easyc Pro.

I want to run the VEX controller but the motors won’t run without the transmitter on.

How do you get around that?

I am playing with the robot and the CMUCAM but don’t want to have transmitter on.

Making an assumption,

NOTE: What I assume is probably wrong.

in EasyC, when you download the code, there is no way to go from enable to disable like there is RobotC. So I’m pretty sure that without the transmitter being on, your robot is in disabled mode and with it on, your code runs.

I haven’t actually gotten to run code in RobotC, but looking at the video, I don’t think one needs the controller.

That’s an assumption. :D.

The enable/disable state is governed by the VEX firmware. Unless you know how to rewrite the firmware, I think you need the transmitter. The timing of the operator controlled mode is syncs itself to the transmitter when it finds a signal, and this is the mode where motor udpates are run because the timing is regulated. Basically, what is called Autonomous() in EasyC is called user_routines_fast.c in the default code, and what is called OperatorControl() is called user_routines.c. The user_routines_fast.c code runs as fast as it is able to, while the user_routines.c code runs once every 18.5 ms. This 18.5 ms cycle is synced to the transmitter’s update rate, also at 18.5 ms, when the transmitter is turned on. Because motor signals are also time critical, and update at 18.5 ms. all of the motors signals are handled in user_routines.c regardless of whether or not they’re sent in autonomous or operator control. However, user_routines.c does rely on the transmitter, so motors will not run without that code being synced up.

Using MPLAB C you can run easily without the transmitter by having the code force autonomous operation.
I haven’t used a transmitter in any of my workshops since the Vex kits came out.

However, EasyC doesn’t have a direct mechanism to do this.

Thanks guys for the input.

I seem to recall that there are two set of “functions” for turning motors/servos on; and that one of them required the transmitter to be on and the other didn’t?

It’s worth a try before you dive into the MPLAB stuff, unless that is something you want to do anyway.


If you use a standard project in easyC Pro for the vex the robot can be run 100% autonomously and doesn’t need the transmitter. I think it may be a bug in an earlier version of the WPILib I believe it was fixed a couple versions ago. You can update for free at

If you want to check if the transmitter is running for an enable / disable switch then you can call ReceivingData(unsigned char port) it returns a true/false . The port is which transmitter port you have connected.

I’ll have to update my EasyC Pro.

Using MPLAB C you can run easily without the transmitter by having the code force autonomous operation.

As far as I know, you must have a transmitter turned on to trigger autonomus mode.

The way the field control works is turning the transmitter on and off to cycle through the robot “control states”.

I seem to recall that there are two set of “functions” for turning motors/servos on; and that one of them required the transmitter to be on and the other didn’t?

There is an option on who is the controller of the motors:

* FUNCTION NAME: Setup_Who_Controls_Pwms
* PURPOSE:       Each parameter specifies what processor will control the pwm.  
* CALLED FROM:   User_Initialization
*     Argument             Type    IO   Description
*     --------             ----    --   -----------
*     pwmSpec1              int     I   USER/MASTER (defined in ifi_aliases.h)
*     pwmSpec2              int     I   USER/MASTER
*     pwmSpec3              int     I   USER/MASTER
*     pwmSpec4              int     I   USER/MASTER
*     pwmSpec5              int     I   USER/MASTER
*     pwmSpec6              int     I   USER/MASTER
*     pwmSpec7              int     I   USER/MASTER
*     pwmSpec8              int     I   USER/MASTER
* RETURNS:       void
static void Setup_Who_Controls_Pwms(int pwmSpec1,int pwmSpec2,int pwmSpec3,int pwmSpec4,
                                    int pwmSpec5,int pwmSpec6,int pwmSpec7,int pwmSpec8)
  txdata.pwm_mask = 0xFF;         /* Default to master controlling all PWMs. */
  if (pwmSpec1 == USER)           /* If User controls PWM1 then clear bit0. */
    txdata.pwm_mask &= 0xFE;      /* same as txdata.pwm_mask = txdata.pwm_mask & 0xFE; */
  if (pwmSpec2 == USER)           /* If User controls PWM2 then clear bit1. */
    txdata.pwm_mask &= 0xFD;
  if (pwmSpec3 == USER)           /* If User controls PWM3 then clear bit2. */
    txdata.pwm_mask &= 0xFB;
  if (pwmSpec4 == USER)           /* If User controls PWM4 then clear bit3. */
    txdata.pwm_mask &= 0xF7;
  if (pwmSpec5 == USER)           /* If User controls PWM5 then clear bit4. */
    txdata.pwm_mask &= 0xEF;
  if (pwmSpec6 == USER)           /* If User controls PWM6 then clear bit5. */
    txdata.pwm_mask &= 0xDF;
  if (pwmSpec7 == USER)           /* If User controls PWM7 then clear bit6. */
    txdata.pwm_mask &= 0xBF;
  if (pwmSpec8 == USER)           /* If User controls PWM8 then clear bit7. */
    txdata.pwm_mask &= 0x7F;
* FUNCTION NAME: User_Initialization
* PURPOSE:       This routine is called first (and only once) in the Main function.  
*                You may modify and add to this function.
*                The primary purpose is to set up the DIGITAL IN/OUT - ANALOG IN
*                pins as analog inputs, digital inputs, and digital outputs.
* CALLED FROM:   main.c
* ARGUMENTS:     none
* RETURNS:       void
void User_Initialization (void)

<..... snip about 25 lines ...>

/* SEVENTH: Choose which processor will control which PWM outputs. */

/* EIGHTH: Set your PWM output type.  Only applies if USER controls PWM 1, 2, 3, or 4. */
  /*   Choose from these parameters for PWM 1-4 respectively:                          */
  /*     IFI_PWM  - Standard IFI PWM output generated with Generate_Pwms(...)          */
  /*     USER_CCP - User can use PWM pin as digital I/O or CCP pin.                    */

But I think that’s the PWM pulse timing, not if the motor drive is enabled. It’s making changes in the Tdata structure. Maybe someone from IFI can add some light, but as far as I know the transmitter needs to be on to enable the motors to move.

Nope, Haven’t turned on most of my vex controls in years.

In EasyC Pro follow Adam’s directions.

In MPLAB C just needs one line of code to tell the master you want to be in autonomous mode:

txdata.user_cmd = 2;  // set to zero instead for user control

Interesting. I guess the syncing just realigns the motor signals. Does anyone know how to do this manually in WPILib (not using EasyC)? I’m using the most current version of WPILib that I know of (from January 22, 2008, latest I can find), but there are no functions that allude to fail-safing the motor outputs, nor anything in the documentation. I do eventually want to learn the default code, but that day is not today. If you don’t know the way to do it directly in the WPILib C, do you know what the setting is in EasyC? Danke.

I found my problem, something killed my master code. I updated the code and now it works fine and works with or without transmitter.