USB-to-Serial Module based coders cable

[pboese]

Quick update: I can't get this PIC chip to operate as I originally envisioned with dual clocks. It can do it, but only for low power, low frequency modes. So the maximum baud I've been able to calculate that will be common to both the DC and this USB-Serial device is 781249 and 800000 respectively. That's 2.4% baud error, but acceptable. So not as speedy as I had originally hoped, but not bad either. I'll be building up a prototype for actual tests over the next week or so. The hardware is pretty simple, but the software/firmware for the PIC will take a little while to get working properly.

The code is based on the Microhip USB CDC demo/tutorial so it will look like a serial/modem type of device to Windows 2K/XP, and Linux kernel 2.6+. Not sure about OS/X.

If this works it will probably be sold as a hobbyist type of kit since it will be using Microchip's USB VID/PID for their CDC demo. I intend to install the bootloader into the PIC so the device will be field upgradeable (firmware wise) via the USB port.; e.g. a real software hackers playtoy! All the development tools (IDE, assembler, C compiler, etc.) are available from Microchip online for free!

[pboese]

I don't like not being able to run the connection speed at 1.56M baud, therefore I have decided to add an external USART in the form of a second PIC microcontroller. Communications between the two PICs will be via the Serial Peripheral Interface (SPI). It keeps the interface between the chips simple (3 lines) and gives me the oppourtunity to customize the operation of the device to this application. So now the two main parts are the PIC18F2550 (4Mhz Xtal/48Mhz Pll)which handles the USB interface and the PIC18F252 (25Mhz Xtal) which will be programmed to serve as a serial USART.

A sample part is on its way from Microchip.

[kgenthe]

What/where is "MKE" WI? I'm from Green Bay

[pboese]

What/where is "MKE" WI? I'm from Green Bay

MKE is an abbreviation for Milwaukee that I've seen used by the postal, shipping and airline industries. It's short but sweet, no?

[pboese]

I've had an interesting thought. It's about using the Maple bus, that's the gameport connectors on the front of the DC instead of the serial port. Right now it's just an idea, but I'm looking at the technical issues to see if there would be any advantage. The Maple bus runs at 2M bps, that's bits per second, but the bandwidth is shared by all the connected devices. That means that the overall throughput would be less than 2M bps. I base that statment on other considerations like protocol overhead and the fact that the Maple bus communications are totally host initiated and half duplex. It's similar to USB protocols in many ways. I'll probably try to rig up a fixture to snoop on the Maple bus transactions on one of the ports for the fun of it.

BTW I just received the 2nd PIC today, so I can begin some PIC to PIC comm experiments. I also tried connecting the prototype device to a Linux machine to see if it would work. So far no luck. I need to review the Linux cdc-acm driver code to find out what's going on.

[Kochise]

http://www.beyondlogic.org/usb/ftdi.htm : RS422/485 to 2000Kbps !

Sounds interresting ? Maybe a chip member of the same family should overshoot this one ?

Kochise

[kgenthe]

Kind of figured Milwaukee... oh well, Wisconsin, represent!

[pboese]

http://www.beyondlogic.org/usb/ftdi.htm : RS422/485 to 2000Kbps !

Sounds interresting ? Maybe a chip member of the same family should overshoot this one ?

Kochise

Ack! That page is really old, I used a FT232BM in the previous design. Nice chip really, but not ideal for this application; thus I'm back to the drawing board

I really despise beyondlogic, those pages drop "pop-unders" with Firefox no-less! Damn advertisements.

[Kochise]

Don't see none of them, using Opera in F12 -> 'Block unwanted pop-up' setting

Kochise

[pboese]

Don't see none of them, using Opera in F12 -> 'Block unwanted pop-up' setting

Kochise

I tried Opera Once about two years ago. Maybe I'll give it another shot.