USB CDC Communications for Dummies!

[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