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questions about example program ex_usb_hid.c

 
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hemnath



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questions about example program ex_usb_hid.c
PostPosted: Sun May 25, 2014 11:21 pm     Reply with quote

Hi,
I've been studying the USB and gone through the example code ex_usb_hid.c.

I have a question,
ADC on PIN AN0: Whether the ADC value will not exceed 255? If i want to send 1023, will it not send?

Thanks in advance.
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Mon May 26, 2014 1:31 am     Reply with quote

The example, configures the ADC for low accuracy only.
#device ADC=8

and

ADC_CLOCK_INTERNAL

This gives an 8bit low accuracy value.

No, you could not send 1023, The example PC code expects to only receive single bytes for simplicity/speed.

To send a larger value, the code at the PC end would need to be re-written to expect two bytes for each value, and the transmission code would have to switch the ADC to a more accurate mode, and send this as two bytes.

'HID' code is originally designed for things like joysticks (human interface devices), with the assumptions this brings.
hemnath



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PostPosted: Mon May 26, 2014 2:04 am     Reply with quote

Thanks Ttelmah for the explanation.
hemnath



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PostPosted: Mon May 26, 2014 2:08 am     Reply with quote

I'm asking in general, not considering this example.

This example sends 8 bit(1 byte) data in a single pipe. I'm clear about that.

Is it possible to send a 16 bit value through the single pipe?

Example:
out_data[0]=250; // It can be sent.

Will it be?
out_data[0]=1000;

Will USB allows 16 bit value?
E_Blue



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PostPosted: Wed May 28, 2014 6:56 am     Reply with quote

No, USB sends only single bytes, that means 0 to 255 decimal values.
To send 16bit value you must two break the value in to two bytes and then put one byte on [0] and the other byte in [1]

Something like

Code:

out_data[0]=make8(1000,0);
out_data[1]=make8(1000,1);


Of course on PC side you will need to put them together again in correct order by software.
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hemnath



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PostPosted: Fri May 30, 2014 5:32 am     Reply with quote

Thanks E_Blue..

What is Endpoint in USB?

Why there is maximum of 16 Endpoints.
Please clarify.
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