USBout problem

[rubisharmax]

Hi,

I'm using the following code to send data over USB which I learned from this thread: http://www.picbasic.co.uk/forum/showthread.php?t=5806

DEFINE    OSC 48


Buffer    VAR BYTE[1]
Cnt       VAR BYTE
counter   VAR WORD


ADCON1 = 15               ' Set all I/Os to Digital      
CMCON = 7                 ' Disable Comparators
Cnt = 1


USBInit                   ' Initialize USART


' Main Program Loop
Loop:
    
    USBService        ' Must service USB regularly
    Buffer(0)=50
    USBOut 3, Buffer, Cnt, loop
    Buffer(0)=60
    USBOut 3, Buffer, Cnt, loop
    goto loop

end

I check the received data on HyperTerminal but it only shows getting "2"s which means that Buffer[0] is always 50 and never takes the value 60. Could you help me with this problem please, what's the problem in my code? It's supposed to send 50 and 60 in an alternating pattern which correspond to "2" and "<" according to ASCII table.

Regards

[Darrel Taylor]

USB "Frames" occur at 1ms intervals.
When you send 50, it will have to wait until the next Frame to send 60.

During that time any USBOUT statements will fail, and jump to the specified Label.
Since you only have 1 Label, it always goes back to sending 50. 60 never gets sent.

Using a label for each transmission will help.

' Main Program Loop
Loop1:
    USBService        ' Must service USB regularly
    Buffer(0)=50
    USBOut 3, Buffer, Cnt, loop1

Loop2:
    USBService
    Buffer(0)=60
    USBOut 3, Buffer, Cnt, loop2
goto loop1

[rubisharmax]

Thanks DT, I'll try this code. BTW, does 1ms time interval mean that we can only send 1000 Bytes of data in a second via USB?

[Darrel Taylor]

Each Frame can transfer 64 bytes in Full Speed mode.
So theoretically the transfer rate is 64000 bytes/sec.

However, that rate is not acheivable without using ping-pong buffers, which PBP does not support.
Without ping-pongs, I've measured approximately 56kBytes/sec.

Other devices on the USB bus can reduce that as they use frames for their traffic too.

[rubisharmax]

Thanks a lot for the useful information.