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Connect USB HID with PIC18F4450 Code

Universal Serial Bus (USB) provides a serial bus standard for connecting a wide variety of devices, including computers, cell phones, game consoles, PDA’s, etc.
USB Library contains HID routines that support HID class devices, and also the generic routines that can be used with vendor specified drivers.

USB HID Class

The HID class consists primarily of devices that are used by humans to control the operation of computer systems. Typical examples of HID class devices include :
  • Keyboards and pointing devices, for example: standard mouse devices, trackballs, and joysticks.
  • Front-panel controls, for example: knobs, switches, buttons, and sliders.
  • Controls that might be found on devices such as telephones, VCR remote controls, games or simulation devices, for example: data gloves, throttles, steering wheels, and rudder pedals.
  • Devices that may not require human interaction but provide data in a similar format to HID class devices, for example, bar-code readers, thermometers, or voltmeters.
Many typical HID class devices include indicators, specialized displays, audio feedback, and force or tactile feedback. Therefore, the HID class definition includes support for various types of output directed to the end user.

Descriptor File

Each project based on the USB library should include a descriptor source file which contains vendor id and name, product id and name, report length, and other relevant information. To create a descriptor file, use the integrated USB HID terminal of mikroC PRO for PIC (Tools › USB HID Terminal). The default name for descriptor file is USBdsc.c, but you may rename it.
  Important :
  • The USB library routines have been changed. Please, have this in mind when migrating projects from previous versions of the compiler.
  • Also, this relates to the descriptor source file, so it is necessary to create a new descriptor file in order to make your project work.

Library Routines

  • HID_Enable
  • HID_Read
  • HID_Write
  • HID_Disable
  • USB_Interrupt_Proc
  • USB_Polling_Proc
  • Gen_Enable
  • Gen_Read
  • Gen_Write

HID_Enable

Prototype void HID_Enable(char *readbuff, char *writebuff);
Description Enables USB HID communication.
Parameters
  • readbuff: Read Buffer.
  • writebuff: Write Buffer.
These parameters are used for HID communication.
Returns Nothing.
Requires Nothing.
Example 
HID_Enable(&readbuff,&writebuff);
Notes This function needs to be called before using other routines of USB HID Library.

HID_Read

Prototype char HID_Read(void);
Description Receives message from host and stores it in the Read Buffer.
Parameters None.
Returns If the data reading has failed, the function returns 0. Otherwise, it returns number of characters received from the host.
Requires USB HID needs to be enabled before using this function. 
Example 
// retry until success
while(!HID_Read())
  ;
Notes None.

HID_Write

Prototype char HID_Write(char *writebuff, char len);
Description Function sends data from Write Buffer writebuff to host.
Parameters
  • writebuff: Write Buffer, same parameter as used in initialization;
  • len: specifies a length of the data to be transmitted.
Returns If the data transmitting has failed, the function returns 0. Otherwise, it returns number of transmitted bytes.
Requires USB HID needs to be enabled before using this function.
Example 
// retry until success
while(!HID_Write(&writebuff,64))
  ;
Notes Function call needs to be repeated as long as data is not successfuly sent.

HID_Disable

Prototype void HID_Disable(void);
Description Disables USB HID communication.
Parameters None.
Returns Nothing.
Requires USB HID needs to be enabled before using this function. 
Example 
HID_Disable();
Notes None.

USB_Interrupt_Proc

Prototype void USB_Interrupt_Proc(void);
Description This routine is used for servicing various USB bus events. Should be called inside USB interrupt routine.
Parameters None.
Returns Nothing.
Requires Nothing.
Example 
void interrupt() {
  USB_Interrupt_Proc();
}
Notes Do not use this function with USB_Polling_Proc, only one should be used. To enable servicing through interrupt, USB_INTERRUPT constant should be set (it is set by default in descriptor file).

USB_Polling_Proc

Prototype void USB_Polling_Proc(void);
Description This routine is used for servicing various USB bus events. It should be periodically, preferably every 100 microseconds.
Parameters None.
Returns Nothing.
Requires Nothing.
Example 
while(1) {
  USB_Polling_Proc();
  kk = HID_Read();
  if (kk != 0) {
    for(cnt=0; cnt < 64; cnt++)
      writebuff[cnt]=readbuff[cnt];
  HID_Write(&writebuff,64);
  }
}
Notes Do not use this functions with USB_Interrupt_Proc. To enable servicing by polling, USB_INTERRUPT constant should be set to 0 (it is located in descriptor file).

Gen_Enable

Prototype void Gen_Enable(char* readbuff, char* writebuff);
Description Initialize the USB module of the MCU.
Parameters
  • readbuff: Read Buffer.
  • writebuff: Write Buffer.
Returns Nothing.
Requires USB needs to be enabled before using this function. 
Example 
Gen_Enable(&readbuff,&writebuff);
Notes None.

Gen_Read

Prototype char Gen_Read(char *readbuff, char length, char ep);
Description Generic routine that receives the specified data from the specified endpoint.
Parameters
  • readbuff: Received data.
  • length: The length of the data that you wish to receive.
  • ep: Endpoint number you want to receive the data into.
Returns Returns the number of received bytes, otherwise 0.
Requires USB needs to be enabled before using this function. 
Example 
while(Gen_Read(readbuff,64,1)==0)
  ;
Notes None.

Gen_Write

Prototype char Gen_Write(char* writebuff, char length, char ep);
Description Sends the specified data to the specified endpoint.
Parameters
  • writebuff: The data that you want to send.
  • length: the length of the data that you wish to send.
  • ep: Endpoint number you want to send the data into.
Returns Returns the number of transmitted bytes, otherwise 0.
Requires USB needs to be enabled before using this function.
Example 
while(Gen_Write(writebuff,64,1)==0)
  ;
Notes None.

Code Example

This example establishes connection with the HID terminal that is active on the PC. Upon connection establishment, the HID Device Name will appear in the respective window. After that software will wait for data and it will return received data back. Examples uses USBdsc.c descriptor file, which is in the same folder, and can be created by the HID Terminal.
  
unsigned char readbuff[64] absolute 0x500;   // Buffers should be in USB RAM, please consult datasheet
unsigned char writebuff[64] absolute 0x540;

char cnt;
char kk;

void interrupt(){
   USB_Interrupt_Proc();                   // USB servicing is done inside the interrupt
}

void main(void){
  ADCON1 |= 0x0F;                         // Configure all ports with analog function as digital
  CMCON  |= 7;                            // Disable comparators

  HID_Enable(&readbuff,&writebuff);       // Enable HID communication

  while(1){
    while(!HID_Read())
      ;

    for(cnt=0;cnt<64;cnt++)
      writebuff[cnt]=readbuff[cnt];

    while(!HID_Write(&writebuff,64))
      ;
  }
}

HW Connection

 

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