Toggling DCD

acidice333 · Joined: 14 Oct 2006 Posts: 33

Trying the USB to Serial thing on my 18f4550 and was wondering Is it possible to toggle the DCD (Data Carrier Detect)?

I need to receive DCD signal on the computer.

Ttelmah · Joined: 11 Mar 2010 Posts: 19541

DCD, in the USB serial emulation, is controlled by the structure usb_cdc_carrier, and the bit in this 'active'. If you set:

usb_cdc_carrier.active=FALSE;

then DCD will be turned off to the PC. Set it 'TRUE' again to turn carrier detect back on.

Best Wishes

acidice333 · Joined: 14 Oct 2006 Posts: 33

Yeah I tried that. well I used =1 instead of =true but it didn't work.

I used the SIOW app to monitor the DCD status and even if I toggle it on and off, the status never changes??

Ttelmah · Joined: 11 Mar 2010 Posts: 19541

Remember you need to send something, or there won't be a transaction to send the change. It is not automatically updated. Classic would be to send a 'break'.

Best Wishes

acidice333 · Joined: 14 Oct 2006 Posts: 33

Yeah I tried that and still no go :( outputtted a char just to see if the program works and it does.

I guess I'll just have to use the FTDI chip instead :(

Im using compiler version 4.120, which I doubt matters.

Ttelmah · Joined: 11 Mar 2010 Posts: 19541

See the problem. The driver is not implementing the 'LINE_STATE_CHANGE' output. If you set the DCD off, and reinitialise, the PC will see it as off, but it depending on how the PC code works, it won't see the line change once it is initialised.
Can't you use RTS/CTS, which is the normal way to stop output?.

Best Wishes

acidice333 · Joined: 14 Oct 2006 Posts: 33

Sadly no :( This legacy device uses DCD

Ttelmah · Joined: 11 Mar 2010 Posts: 19541

It is not terribly hard to add the required part to the USB code. It depends how happy you are with modifying the supplied code....

Best Wishes