Using Velleman K8076/VM134 PIC-programmer with Microchip's Library of Applications: USB programming basics
In my previous blog I described how to install the micro usb driver on Windows 7 64-bits. This blog describes how you can use
Microchip's Libraries of Application without one of Microchip's programmer boards. I use
Velleman's K8076 instead. This device is also available as prebuild
VM134 .
As I browsed through the available applications, I saw the folder "Device - HID - Custom Demos". That immediately got my attention. So I opened the several .NET projects inside. One of the projects is called "HID PnP Demo".
hidpnpdemo screen
StatusBox_txtbx
default text: "Device Not Detected: Verify Connection/Correct Firmware" upon succesfully connecting the device: "Device Found: AttachedState = TRUE" ToggleLEDs_btn
sets flag ToggleLEDsPending which is handled in worker thread.
PushbuttonState_lbl
default text: "Pushbutton State: Unknown" When connected, based on PushbuttonPressed flag it shows:
false: "Pushbutton State: Not Pressed"
true: "Pushbutton State: Pressed" The PushbuttonPressed flag is set in worker thread.
First a 0x81 is send to the device. When the resulting bytes are: 0x81 0x01
it is set to true, when resulting bytes are: 0x81 0x00 it is set to false.
progressBar1 (show ANx voltage )
shows ADCValue which is determined in worker thread
Besides the windows application sources in different programming languages (C#, C++.NET and VB.Net) there is also the firmware part for the project which can be found in:
[location of your microchip library of applications]\USB\Device - HID - Custom Demos\Firmware.
In order to compile this, you need
MLABX and a
C18 compiler for compiling code for the PIC18F4550.
One of the codes that should be on the firmware site is 0x80. So let't do a global search for it and see whether we can find it. One of the files that match is main.c
void ProcessIO(void)
{
//Blink the LEDs according to the USB device status
if(blinkStatusValid)
{
BlinkUSBStatus();
}
// User Application USB tasks
if((USBDeviceState < CONFIGURED_STATE)||(USBSuspendControl==1)) return;
//Check if we have received an OUT data packet from the host
if(!HIDRxHandleBusy(USBOutHandle))
{
//We just received a packet of data from the USB host.
//Check the first byte of the packet to see what command the host
//application software wants us to fulfill.
switch(ReceivedDataBuffer[0]) //Look at the data the host sent, to see what kind of application specific command it sent.
{
case 0x80: //Toggle LEDs command
blinkStatusValid = FALSE; //Stop blinking the LEDs automatically, going to manually control them now.
if(mGetLED_1() == mGetLED_2())
{
mLED_1_Toggle();
mLED_2_Toggle();
}
else
{
if(mGetLED_1())
{
mLED_2_On();
}
else
{
mLED_2_Off();
}
}
break;
case 0x81: //Get push button state
//Check to make sure the endpoint/buffer is free before we modify the contents
if(!HIDTxHandleBusy(USBInHandle))
{
ToSendDataBuffer[0] = 0x81; //Echo back to the host PC the command we are fulfilling in the first byte. In this case, the Get Pushbutton State command.
if(sw3 == 1) //pushbutton not pressed, pull up resistor on circuit board is pulling the PORT pin high
{
ToSendDataBuffer[1] = 0x01;
}
else //sw3 must be == 0, pushbutton is pressed and overpowering the pull up resistor
{
ToSendDataBuffer[1] = 0x00;
}
//Prepare the USB module to send the data packet to the host
USBInHandle = HIDTxPacket(HID_EP,(BYTE*)&ToSendDataBuffer[0],64);
}
break;
case 0x37: //Read POT command. Uses ADC to measure an analog voltage on one of the ANxx I/O pins, and returns the result to the host
{
WORD_VAL w;
//Check to make sure the endpoint/buffer is free before we modify the contents
if(!HIDTxHandleBusy(USBInHandle))
{
w = ReadPOT(); //Use ADC to read the I/O pin voltage. See the relevant HardwareProfile - xxxxx.h file for the I/O pin that it will measure.
//Some demo boards, like the PIC18F87J50 FS USB Plug-In Module board, do not have a potentiometer (when used stand alone).
//This function call will still measure the analog voltage on the I/O pin however. To make the demo more interesting, it
//is suggested that an external adjustable analog voltage should be applied to this pin.
ToSendDataBuffer[0] = 0x37; //Echo back to the host the command we are fulfilling in the first byte. In this case, the Read POT (analog voltage) command.
ToSendDataBuffer[1] = w.v[0]; //Measured analog voltage LSB
ToSendDataBuffer[2] = w.v[1]; //Measured analog voltage MSB
//Prepare the USB module to send the data packet to the host
USBInHandle = HIDTxPacket(HID_EP,(BYTE*)&ToSendDataBuffer[0],64);
}
}
break;
}
//Re-arm the OUT endpoint, so we can receive the next OUT data packet
//that the host may try to send us.
USBOutHandle = HIDRxPacket(HID_EP, (BYTE*)&ReceivedDataBuffer, 64);
}
}//end ProcessIO
As you can see, all the codes used on the Windows side are also used in the switch statement: 0x80, 0x81 and 0x37.
Searching for 0x80
#define mGetLED_1() mLED_1
#define mGetLED_2() mLED_2
#define mGetLED_3() mLED_3
#define mGetLED_4() mLED_4
Ok. So mGetLED1 returns mLED1, mGetLED2 returns mLED2. As you can see there are even 4 getLEDs defined.
#define mLED_1 LATDbits.LATD0
#define mLED_2 LATDbits.LATD1
#define mLED_3 LATDbits.LATD2
#define mLED_4 LATDbits.LATD3
Bingo! I recognize device ports. So there are at least 4 leds, connected to port D0 (pin 19), D1 (pin 20), D2 (pin 21) and D3 (pin 22).
#define sw2 PORTBbits.RB4
#define sw3 PORTBbits.RB5
Ok, so we have two switches attached to RB4 (pin 37) and RB5 (pin 38) where RB5 is the one we need.
WORD_VAL ReadPOT(void)
{
WORD_VAL w;
w.Val = 0;
ADCON0bits.GO = 1; // Start AD conversion
while(ADCON0bits.GO); // Wait for conversion
w.v[0] = ADRESL;
w.v[1] = ADRESH;
w.Val = ADC1BUF0;
return w;
}
So it uses ADCON0. Let's see if we can find that in the "hardwareprofile picdem fsusb.h"
#define mInitPOT()
{
TRISAbits.TRISA0 = 1;
ADCON0 = 0x01;
ADCON2 = 0x3C;
ADCON2bits.ADFM = 1;
}
TRISA0 is used for the A/D conversion which means port A0 (pin 2)
The next challenge is to build a bread board version that can be attached to the PC. Below you can see the schema I created with
gEDA The schema comes with no warranty. Use at your own risk.
USB schema PIC18F4550
And on breadboard:
usb pic18f4550 breadboard
Before connecting it to the computer, always check, double check that you haven't made a mistake in wiring, otherwise you might blow up one or more of your usb ports(!)
usb connector type B
After I modified the source Form1.cs of the windows project, I could capture the A/D conversion and show it in a 'oscilloscope-ish' way.
A/D conversion: playing with screw driver
@paiboon:
Basically it comes down to this:
poll the A/D values in a fixed frequency: see private void FormUpdateTimer_Tick(object sender, EventArgs e) Store the values in an array: private int[] adcValues = new int[1024];
Beware of the bounds of your array: start at position 0 when you reached the end of the array Draw the contents of the array in the paint event: private void paintScope(object sender, PaintEventArgs e) I added downloads for code at:
PIC18F4550 USB Scope speed limits