USB CDC Communications for Dummies!

[Squibcakes]

Want to communicate with your PIC via USB?
Want to install a virtual Commport on your PC?
Want to send serial commands to your PIC?

Its REALLY easy! Here's how.

Get yourself a PIC18F2455/2550/4455 chips that has USB support. And connect the Usb to to your PIC as shown below.

Note if using the USB bus power to power your pic remember that the max current your pic circuit can draw is 100ma! Anymore and you may blow your usb port! If in doubt stick in a fuse, or use external power.

For this demo though you can safely use the Bus Power. Mecanique has a good circuit diagram you can follow here. http://www.mecanique.co.uk/products/...atic-large.gif

Pin Name Cable color Description
1 VCC Red +5 VDC (Vdd)
2 D- White Data - (RC4)
3 D+ Green Data + (RC5)
4 GND Black Ground (Vss)

Once your hardware is setup follow on....

STEP ONE.

In your PBP folder, copy the entire contents of the USB18 folder into a new folder where you store your pic programs;

eg... copy c:\pbp\usb18\*.* c:\cdcdemo

STEP TWO.

Open the USB descriptors file (called USBDESC.asm)
There are three lines of code in there, change the ; so that CDCDESC.ASM is used.

;	include "MOUSDESC.ASM"		; USB descriptors for mouse demo
;	include "JADESC.ASM"		; USB descriptors for Jan Axelson's demo
	include "CDCDESC.ASM"		; USB descriptors for CDC demo

STEP THREE.

Copy this code and save it into the c:\cdcdemo folder and then compile using pbp.

DEFINE    OSC 48

Buffer    VAR BYTE[16]
Cnt       VAR BYTE
B0        VAR BYTE
B1        VAR BYTE

ADCON1 = 15               ' Set all I/Os to Digital      
CMCON = 7                 ' Disable Comparators
Cnt = 16

USBInit                   ' Initialize USART

for b0 = 0 to 15
    lookup b0,["USB CONNECTED!",10,13],B1 
    BUFFER(B0) = B1
    NEXT B0

' Main Program Loop
Loop:
    USBService        ' Must service USB regularly
    USBOut 3, Buffer, Cnt, loop
    goto loop
end

When you compile the above program, PBP fuses the USB18 files in youe cdcdemo folder to generate the neccessary .HEX file. Viola!!
run your progam.

Windows will detect the PIC as a USB device and install the Microchip CDC driver.

STEP FOUR.

Open up Hyperteminal and select the virtual comport that was just installed. you should see USB CONNECTED! repeated.

Congratulations, you can send data from the PIC to the PC via a quasi Serial connection.

Ok How about sending and receiving data?

Program this code below into your pic:

buffer	Var	Byte[16]
cnt	Var	Byte
LED	Var	PORTB.0

Define  OSC     48

	USBInit
	Low LED		' LED off

' Wait for USB input
idleloop:
	USBService	' Must service USB regularly
	cnt = 1	' Specify input buffer size
	USBIn 3, buffer, cnt, idleloop

' Message received
	Toggle LED

outloop:
	USBService	' Must service USB regularly
	USBOut 3, buffer, cnt, outloop

	Goto idleloop	' Wait for next buffer

Again open Hyperterminal and the PIC will echo back the characters that you type (one byte at a time).

Try sending a large text file. Does it keep up?

Wow your becoming an expert now aren't you!

Stay Tuned....
Squib

[Bruce]

Nice work Squib...;o}

[T.Jackson]

Nicely done. Worth a vote...

It would be great to see a lot more practical examples posted. Even better if there's an electrical schematic included as well.

Best Regards,
Trent Jackson

[mister_e]

[Pic_User]

Beautiful, step by step “how to” piece of art. Thank you Squib. Nicely done.
-Adam-

[vacpress]

thanks squib!

you are great.

[ricgar]

Hi Squipcakes

I've followed your instructions for this post and built the schematics attached which are very similar to yours posted (see attached). But once compiled and loaded onto the chip, the chip's power led lights up but the diagnostic led's don't and the PC doesn't even see a device attached to the system. I've checked my connections and they all seem fine. I have also attached the files used to make the hex and the hex (file is the mycdc.hex). I'm using a PIC18f2450 (not the same as in the schematics but same pinning)

What could be the problem??

Thanks

[kirtcathey]

Hi All. Thanks in advance for the help.

I am in a similar situation as the respondent above. Have setup everything with an 18F2550 and when plugged in, device not recognized error appears in XP. Where are the CDC drivers mentioned? A lot of the posts above applaud the project, but when a real implementation question is asked, it gets quiet.

Please, throw the dog a bone!

Regards,
Kirt

[kirtcathey]

Okay, I have got my problems down to matching VID and PID numbers in the mchpcdc.inf file and the VID and PID numbers burned on the PIC (18F2550).

Have looked in cdcdesc.asm, but don't know where to find these values.

Any help?

[kirtcathey]

Well.... I figured out the PID and VID stuff... The values in the cdcdesc.asm file and the values in the inf file of the driver (CDC this time) you are using must match.

After confirming this, XP still recognizes that a USB device is attached, but when I go to install the CDC driver, an XP dialog that says hardware information cannot be found appears.

Any help?

[arniepj]

Its been awhile since I went through the same project, but I don't think you need to modify those files.The pic config settings needs to be correct though.I have attached a project folder with files I did once I had it working.Look through the the files for possible clues,primarily the .bas for the config settings.
It uses a 4mhz crystal.
Good luck

[sputnik77]

arniepj, I cannot get your code working either.

There are no config fuses set in the code, and I do not know what they are supposed to be for this application.

I cannot fing any hints in your code as to how to get it to work.

Any help is much appreciated.

[kirtcathey]

Thanks alot. I popped a 4MHz clock (in place of 12 MHz) and compiled successfully. However, with the same result: the program compiles and the chip is programmed fine. I plug the USB cable into the test PC (and others) and windows will prompt as an unrecognized device. I go into the driver configuration and when I load the .inf file, windows again prompts that there is no hardware information available.

Have gone through the data sheet and fuses very close ... but the same result, which has me wondering about the cdc drivers that I am using for the PC....

[Darrel Taylor]

If it compiles ... The number one cause of USB failure, is improper Oscillator Configurations.

For 4Mhz Crystal ...

@   __CONFIG   _CONFIG1L, _PLLDIV_1_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@   __CONFIG   _CONFIG1H, _FOSC_HSPLL_HS_1H

For 8Mhz Crystal ...

@   __CONFIG   _CONFIG1L, _PLLDIV_2_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@   __CONFIG   _CONFIG1H, _FOSC_HSPLL_HS_1H

For 20Mhz Crystal ...

@   __CONFIG   _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@   __CONFIG   _CONFIG1H, _FOSC_HSPLL_HS_1H

For any of the above configurations, use ...

DEFINE OSC 48

Number two reason ... improper capacitance on VUSB pin. (0.22uF or higher)

#3, connecting +5V from USB port to +5V supply from powered project. (very bad)
Ok, that's not really #3, but it is bad.

[kirtcathey]

This might sound like a crazy question but....

Do I have to install a bootloader of some kind on the 18F2550? If so, where do I get hold of one compatible with the project(s) this thread is about?

This is a great thread. When I get it all going, will package and contribute accordingly.

--Kirt

[kirtcathey]

Thank you Darrel. Here are the configs from the code arnie posted earlier, which is very similar to the configs (except I used a 12 MHz oscillator) that I created earlier according to the data sheet and include file review.

asm
CONFIG_REQ
CONFIG1L = _PLLDIV_1_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
; ; ; USB clock source comes from the 96 MHz PLL divided by 2
; ; [OSC1/OSC2 Src: /1][96 MHz PLL Src: /2] Determines cpu speed
; No prescale (4 MHz oscillator input drives PLL directly)
CONFIG1H = _FOSC_XTPLL_XT_1H & _FCMEN_OFF_1H & _IESO_OFF_1H
; ; ; Oscillator Switchover mode disabled
; ; Fail-Safe Clock Monitor disabled
; XT oscillator, PLL enabled, XT used by USB
CONFIG2L = _PWRT_ON_2L & _BOR_ON_2L & _BORV_2_2L & _VREGEN_ON_2L
CONFIG2H = _WDT_OFF_2H
CONFIG3H = _MCLRE_ON_3H & _LPT1OSC_OFF_3H & _PBADEN_OFF_3H & _CCP2MX_ON_3H
CONFIG4L = _STVREN_ON_4L & _LVP_OFF_4L & _XINST_OFF_4L & _DEBUG_OFF_4L
; Removed ICPRT_OFF_4L used with 18F4550
endasm


Did not have the define statement included though.... try that and see soon.
Also, noticed that your oscillator settings were HS instead of XT.

--Kirt

[Darrel Taylor]

If you're trying to use the new style CONFIG with PBP, you should be aware that it can't be placed in your program.
It has to be the first thing loaded, which means it must be in a file that gets loaded before the PBP library. (Not fun)

The original __CONFIG statements are still the way to set configs with PBP.
In other words, please delete what you just posted from your program, and follow the suggested __CONFIG style.

Also, noticed that your oscillator settings were HS instead of XT.

HS mode will always drive a crystal that might qualify for XT mode. The reverse is not always true. I err on the Cautious side.

[kirtcathey]

Thank you Darrel.

I was going through that the other day and the only way I could get code to compile is the way it is written now... but apparently not compiling correctly.

When I use the __config statements, the following appears rather consistently.

AUTO2550.ASM 72 : Overwriting previous address contents (0000)
Error[118] C:\PROJECTS\KEYFER\AUTO2550\AUTO2550.ASM 72 : Overwriting previous address contents (0001)

This doesn't require a CDC bootloader for the PIC, does it? Also noticed that the cdc windows drivers only have an .inf file and a .cat file, but no .sys file.

--Kirt

[Darrel Taylor]

There we go. That one must be #3

What to do if i get "overwriting previous address content" error message? (mister_e)
http://www.picbasic.co.uk/forum/show...75&postcount=5

[kirtcathey]

Awesome!! That was number 3! Still with the OSC define statement, but will put that in for completeness sake! All works. Will post a detailed 'my experience' in a few.

[kirtcathey]

Okay.... I got this puppy working with a bit of help from Darrel through the posts that lead up to this.

Attached is the MPLAB project file and supporting files. The biggest stickler has been getting the configurations correct for the oscillator selection. So the rule going forward for my projects is to comment out the configuration statements in the PBP devicexxxxx.inc files and declare them in the program.

Enjoy! Will be looking at this often as now I am moving onto inputs and other device profiles.... hopefully!

[sputnik77]

I know to look out for all of the above and im very careful with setting configs on any 18 series device as there is a lot to them, however none of the above is my problem.

I cannot even get a confirmed working hex file to work without the dredded "Unknown Device" error, with EXACT hardware even.

Ive tried many different cables, ports, PC's etc. to no avail.

I always use .47uF caps on VUSB, as I have a hundreds of them.

Im about done with trying to get USB working and just continue on with the FTDI solution.

[kirtcathey]

Are you getting it to recognize the device when you initially plug into your computer?

This is the most straightforward and easiest to run so far. It is based on SquibbCake's code in the first posting.

Arnie >> What was your code supposed to do? When I thought I got it working (which it does for the most part), it was blowing a bunch of "B" and special characters across the screen. But upon closer review of your code, it looks like it is looking for user input, then sending data out on USART TX pins. Can you tell us how it is supposed to function and include a link to a similar schematic?

[kirtcathey]

I have gone throught the microchip document fairly thoroughly but have a few questions about some of the PicBasic Pro commands. In the USBIN and USBOUT functions, the first argument is endpoint. What is this referring to? How is that number determined?

[arniepj]

The code is a test program and actually works with a VB6 interface and yes it is looking for commands.The usart output was initially just to let me know the code was running.You can have serial data simultaneously on the pc's comport and the virtual comport(usb).From a terminal program send MX8 to start the usb xmit and MX9 to stop.If you want the VB code http://www.picbasic.co.uk/forum/show....php?t=7372.If you think the CDC demo was fun,Hid is even better.

[Andre_Pretorius]

Can sombody please give me a hint what i am do-ing wrong i keep getting the following error
C:\PBP246\PIC18EXT.BAS ERROR Line 12: Redefinition of VAR.
Here is the code i use

INCLUDE "MODEDEFS.BAS"
INCLUDE "18F4550.BAS"		; USB descriptors for CDC demo

DEFINE OSC 20				' Define crystal as 20Mhz

'Define ACDIN parameters
Define ADC_BITS 10 			' Set number of bits in result
DEFINE ADC_CLOCK 3 			' Set clock source ( 3 = RC )
DEFINE ADC_SAMPLEUS 50 		' Set sampling time to micro-seconds

'This Part set PORTA 0-3 an analog inputs,4 as digital 
TRISA = %00011111 			'set PORTA 0-5 as inputs
ADCON1 = %00001010 			'ADC use vss and vdd as ref.
ADCON2 = %10000111			'FRC (clock derived from A/D RC oscillator),Right justify output


TRISD = %00001111			'Set port d 0-3 as inputs and 4-7 as outputs
TRISB = %10011000

'**************************************Variables*********************************************
buffer	Var	Byte[16]
cnt	Var	Byte
LED	Var	PORTD.4

USBInit
Low LED		' LED off

'**************************************Main Program******************************************
' Wait for USB input
idleloop:
	USBService	' Must service USB regularly
	cnt = 1	' Specify input buffer size
	USBIn 3, buffer, cnt, idleloop

' Message received
	Toggle LED

outloop:
	USBService	' Must service USB regularly
	USBOut 3, buffer, cnt, outloop

	Goto idleloop	' Wait for next buffer


END

[arniepj]

Comment out INCLUDE "18F4550.BAS and add the following files to the project folder.It compiled fine for me and connected to the pc usb,but your code only flashes an led.
CDCDESC.ASM
usb18.asm
18F4550.BAS
USBDESC.ASM
usb18.inc
usb18mem.asm

[Andre_Pretorius]

Thank you got it running, the problem seemed to be that my pic basic pro was installed in PBP246 and not PBP as one of the references needed it to be, Just fixing the path seemed to repaired everything

[kirtcathey]

Have a very basic question that I want to confirm before going forward...

In the PBP manual, USBIN is described as:

++++++++++++++++++++++++++++++++++
USBIN Endpoint, Buffer, Countvar, Label

Get any available USB data for the Endpoint and places it in the Buffer. Buffer must be a byte array of suitable length to contain the data. Countvar will contain the number of bytes transferred to the buffer. Label will be jumped to if no data is available.
++++++++++++++++++++++++++++++++++

It was my understanding that with or without data, that this function always went to Label. Then within Label we perform a test to see if Buffer has new data and route execution from there.

However, the way that the PBP manual describes it is that if no data is input, then program execution jumps to Label.

Which one is it? Does this function always go to Label after reading 8 bytes (or however many specified during HID config. and specified in CountVar) even if there was or was not any input? Or, does this function only jump to Label when no bytes are read from the bus?

[sputnik77]

Do any of you have a working hex for a 2550 on a 20MHz crystal that I can try?

I have tried everything I have found and still cannot get anything to work. I always get "Unknown Device" error no matter what.


The vendors of the compilers really need to give more concise information on USB communications.

[kirtcathey]

I was consistently getting USB device recognition when I connected, but ended with an unknown device when I did not have the configuration directives set appropriately. Read the above thread between Darrel and myself. Or, you can put in a 4MHz chip and just use the code I posted a couple days ago...

[sputnik77]

OK, I was finally able to get this working.

I was using the USBTEST files above.

I added the extra configs for the write protect stuff that was not in the code and VOILA!!!, it works now.

It seems to be an issue with the PicKit2. It barks at you if those configs are not included, it usually isnt an issue as long as the important ones are defined. However in this case I assume since they were missing , the PicKit2 changed some of the needed configs to something incompatible for some reason.

This should not be the issue, however it works. I removed the extra configs and it doesnt work, add them and its just fine!!!

Now to figure out how to get data INTO the pic.

[sputnik77]

Also, for 20mhz crystal/resonator, you MUST change the osc type to HS instead of XT.

HS will not work on 4Mhz, and vise versa.


SO,
here is what to do to get it working, "for sure". It seems to work for some with different setting however.

Ensure PPLDIV is 1 for 4Mhz, 5 for 20MHz
Ensure osc type is XT for 4MHz and HS for 20MHz
Include ALL config options.

After experimenting fpr days on end these seem to be the things that affect it most, for me anyway.

[sputnik77]

Have a very basic question that I want to confirm before going forward...

In the PBP manual, USBIN is described as:

++++++++++++++++++++++++++++++++++
USBIN Endpoint, Buffer, Countvar, Label

Get any available USB data for the Endpoint and places it in the Buffer. Buffer must be a byte array of suitable length to contain the data. Countvar will contain the number of bytes transferred to the buffer. Label will be jumped to if no data is available.
++++++++++++++++++++++++++++++++++

It was my understanding that with or without data, that this function always went to Label. Then within Label we perform a test to see if Buffer has new data and route execution from there.

However, the way that the PBP manual describes it is that if no data is input, then program execution jumps to Label.

Which one is it? Does this function always go to Label after reading 8 bytes (or however many specified during HID config. and specified in CountVar) even if there was or was not any input? Or, does this function only jump to Label when no bytes are read from the bus?

I have some of the same questions. What IS and endpoint anyway???


In my findings the above example from the manual is backwards. It will only jump to the label if the buffer is FULL. It seems to sit and wait until the specified number of bytes have been received.

[test153]

Note if using the USB bus power to power your pic remember that the max current your pic circuit can draw is 100ma! Anymore and you may blow your usb port! If in doubt stick in a fuse, or use external power.

As far as I know a USB 2.0 device can draw upto 500mA once communication is established and the host grants the request for drawing more power, otherwise the device is only able to get 100mA from the host. I doubt that you will blow the USB port if you draw more then 100mA.

[ricgar]

Hi Guys

I'm pretty new to all of this, but here's my attempt.

I've attached a schematic of the device i am using.

What i am attempting to make here is some sort of USB to Serial Port Converter.

The code i loaded onto the chip is as follows:

'****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2009 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 2009/01/02                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
@   __CONFIG	_CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@	__CONFIG	_CONFIG1H, _FOSC_HSPLL_HS_1H & _FCMEN_OFF_1H & _IESO_OFF_1H
'_CONFIG1H, _FOSC_XTPLL_XT_1H 
@	__CONFIG	_CONFIG2L, _PWRT_ON_2L & _BOR_ON_2L  & _BORV_28_2L  & _VREGEN_ON_2L
@	__CONFIG	_CONFIG2H, _WDT_OFF_2H
@	__CONFIG	_CONFIG3H, _MCLRE_ON_3H & _LPT1OSC_OFF_3H & _PBADEN_OFF_3H & _CCP2MX_ON_3H
@	__CONFIG	_CONFIG4L, _STVREN_ON_4L & _LVP_OFF_4L & _XINST_OFF_4L & _DEBUG_OFF_4L

' ****************************** Configure Hardware *********************************************
trisb = %11111100
trisc = %10111111       	' Set TX (PortC.6) to out, rest in
spbrg = 25            		' Calculate ((CPU speed mhz/Baud)/16)- 1  25 = 115200 baud  EX:((48000000/115200)/16)-1
rcsta = %10010000       	' Enable serial port and continuous receive
txsta = %00100000       	' Enable transmit and asynchronous mode/brgh = 0 bit 2
baudcon =%00001000			' Bit3 = 1: High speed usart 16 bit  

'***************************** Variables ******************************************
USBBufferTX Var Byte[1]
USBBufferRX var Byte[1]
USBBufferCount Var Byte
SerBufferTX Var Byte
SerBufferRX var Byte[1]
BufferRX var Byte
SerBufferCount Var Byte
Indexer var byte
Xmit_Start var bit									' Start serial data transmission
Status_Bits var byte								' Status bits to Pc
Data_Delay var word									' Delay for dataout
Data_Out var word									' Data 

Status_Bits = 0

LED	Var	PORTB.1

Define  OSC     48

	USBInit
	high led
	pause 1000
	Low LED		' LED off
    USBService

    for Indexer = 0 to 0
	   USBBufferRX[Indexer]= 0
    next

    usbbuffercount = 1
    
    
main:
    goSUB usb_rx
    goSUB com_rx
goto main    

	' Transmit USB Data     
USB_TX:
					' TX buffer size
USBService 
USBOut 3, serBufferrX, USBBufferCount, main 			' Transmit data		
RETURN

	' Receive USB Data 
USB_RX: 
USBService 											
USBIn 3, USBBufferRX, USBBufferCount, exitsub 		' Receive data if available,then exit
serbuffertx=usbbufferrx[0]
goSUB com_tx
return
'GOSUB Main


'Serial Receive

COM_RX:
hserin 1, exitsub, [bufferrx]
serbufferrx[0]=bufferrx
goSUB usb_TX
goSUB main

'Serial Transmit
COM_TX:
hserout [serbuffertx]
RETURN

exitsub:
return

Now this code compiles and i can connect via a hyperterminal to both the USB virtual and the physical Serial port. However if i enter anything in either of hyperterminals, it gives nothing and after a while of constant typing the hyperterminals start freezing on me. So i take it i've done something horrifically wrong.

Any suggestions?

[mister_e]

this section

COM_RX:
hserin 1, exitsub, [bufferrx]
serbufferrx[0]=bufferrx
goSUB usb_TX
goSUB main

I guess you want a Return there.

And when you deal with HSEROUT/HSERIN, you should use DEFINEs, unless, it will use default 2400 Bauds baudrate.

AND you must add DEFINE OSC 48 at the top of your code as well.

That should be enough to start

[ricgar]

Hi Mister_e

Thanks for the response. I did already have a DEFINE OSC 48 already near start of the code, i have changed it to be return instead of GoSub Main. Thanks. As for your quote below

this section
you should use DEFINEs, unless, it will use default 2400 Bauds baudrate.

Would you be able to provide a bit more detail as regards the DEFINEs you mention, i have no clue what you mean by that.

Thanks

[mister_e]

DEFINE for HSEROUT are explained in the PBP manual

The serial parameters and baud rate are specified using DEFINEs:

' Set receive register to receiver enabled
DEFINE HSER_RCSTA 90h

' Set transmit register to transmitter enabled
DEFINE HSER_TXSTA 20h

' Set baud rate
DEFINE HSER_BAUD 2400

' Set SPBRG directly (normally set by HSER_BAUD)
DEFINE HSER_SPBRG 25

HSEROUT assumes a 4MHz oscillator when calculating the baud rate. To maintain the proper baud rate timing with other oscillator values, be sure to DEFINE the OSC setting to the new oscillator value.

In your case, the DEFINE list would look something like

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_SPBRG 25  ' 115200 Baud @ 48MHz, 0.16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

HTH

[davids]

DEFINE OSC 48

Buffer VAR BYTE[16]
Cnt VAR BYTE
B0 VAR BYTE
B1 VAR BYTE
led var porta.3

ADCON1 = 15 ' Set all I/Os to Digital
CMCON = 7 ' Disable Comparators
Cnt = 16

USBInit ' Initialize USART
start:
for b0 = 0 to 15
lookup b0,["USB CONNECTED!",10,13],B1
BUFFER(B0) = B1
NEXT B0
gosub send
ledl:
high led
pause 1000'(when i have delay nothing is working)
low led

afterled:
for b0 = 0 to 15
lookup b0,["closed led",10,13],B1
BUFFER(B0) = B1
NEXT B0
gosub send
goto start

send:
USBService ' Must service USB regularly
USBOut 3, Buffer, Cnt,send
return
end