Help required for interfacing 18f4550 with usb gprs modem

[zeeshan ahmed]

Hi all,
I'm new to ccs forum. I need help regarding AT command for GPRS modem. I want to transmit data. I have to interface gprs modem through USB. I know how to program microcontroller for usb interfacing. Right now I need help regarding AT command set. Plz help..ASAP.

regards
Zeeshan

[bkamen]

First question:


Is the GPS a USB DEVICE or HOST.

See... You can't hook a PIC in the USB DEVICE mode to another USB DEVICE. It's how USB was designed.

So to fix the problem of the PDA (as an example) that might be a DEVICE or maybe a HOST.. they came up with USB OTG. (On-The-Go).

If your USB GPS is a DEVICE, then you'd need a PIC with USB OTG ability.

So select a PIC with that knowledge once you've figured out which type of USB device your GPS is.

Also, consider getting a Serial (RS232) based GPS. Interfacing is MUUUUUCCCCHHH easier.

Are you required to use that USB based GPS?

-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D

[zeeshan ahmed]

Thanks for your reply.

Actually gprs is a usb device... and I want to use pic 18f4550 as a host device and will implement TCP/IP stack in pic...but you mention that PIC18f4550 does not have hosting capability. So please let me know which PIC18 series controller has OTG capability. I searched for the PIC controllers which have OTG capability. PIC32 Series have this feature. But I can't use pic32 series in my project.

Again thanks for your time.

[Ttelmah]

Understand that a USB host, requires quite a lot of work, and a lot of code. This is (in part) why it is reserved for larger/faster chips.
There are several 24J chips with this ability, rather than PIC32.
Why do you talk about TCP/IP stack?. A USB stack, is not a TCP/IP stack, and is a lot more complex.
Alternatively, you can add an external host controller to just about any PIC (you don't need a USB PIC), by using the FTDI 'Vinculum'. Advantage here is that the stack is already written for you.
Be aware, that quite a few USB GPRS devices, will also talk using serial connections (they detect one pin of the USB connector being pulled to a different level, and switch to a serial emulation - similar to how most modern keyboards work, switching to USB, or PS/2 connections). Alternatively, there are several serial GPRS devices on the market. Using serial will probably be several _weeks_ quicker, in terms of code development....

Best Wishes

[zeeshan ahmed]

Thanks for your reply....
First i correct u that i will implement TCP/IP stack for GPRS module...here i m seeking help regarding interfacing a USB GPRS modem(device) with PIC(host).
i go through the data sheet of PIC24FJ256GB110 ...and it has OTG feature.

Thanks

[zeeshan ahmed]

Is it possible to make a usb device e.g pic18f4550; a usb host,
by changig the driver file?
please let me know....ASAP
thanks

[bkamen]