Cp2102

Thric

Hey, I'm creating a PCB and i'm trying to add a USB programming port directly on to it (this is my first time ever making my own USB circuit). At first i was looking at FT232RL chip because parallax has documentation over its circuitry but i find the chip consuming too much space. I read a thread on using the CP2102 from silabs to program the prop and was wondering if anyone could help me understand the connections involved.
Thanks
~Osi

Mike Green

You need to supply the link to the thread so we don't have to look it up (and maybe look at the wrong thread) as well as a link to the CP2102 datasheet. Essentially, you need normal receive data and transmit data lines with 3.3V logic levels. You need a ground line (Vss) and a reset line (active low) that's triggered (with a brief pulse) when the virtual serial port goes from /DTR to DTR.

StefanL38

I bought a small PCB that adapts to 0,1 inch-pitch of the PINs and tested it with a DIP40 propeller on a breadboard and a copper-dot PCB
worked both well.

The CP2102 is powered through USB and includes a 100mA 3.3V supply.
To create the reset-impulse you have to insert a 0,1µF capacitor between DTR-line and the Reset-Input-Pin of the propellerchip

datasheet can be found here.
http://www.silabs.com/Support%20Documents/TechnicalDocs/cp2102.pdf

keep the questions coming
best regards

Stefan

Thric

Sorry for the vague references; heres a link to the CP2102 datasheet: http://www.silabs.com/Support%20Documents/TechnicalDocs/cp2102.pdf
and heres the link to that thread that i found:
http://forums.parallax.com/showthread.php?92086-IDE-only-seems-to-use-FTDI-interface-why-not-standard-coms-ports&highlight=cp2103
Thanks for the help.
~Osi

Thric

Wow, you blink for a second and the answer comes before the question . Thanks for the help. So if i understand what your saying is that all I need are the 2 required caps. (in the datasheet) and just need to add a 0.1uf cap from the DTR to the reset pin? Sounds alot simpler than the FT232RL, why isn't the CP2102 chip used in the prop plug??

Mike Green

The CP2102 isn't used in the PropPlug because FTDI was first with a USB to serial chip that worked reliably, was simple to use, and came with I/O drivers for all 3 major OSs, Windows, Linux, and the MacOS. FTDI has consistently updated the chip in a compatible way making it even simpler to use. For a long time, the CP2102 would only work with Windows, another reason for sticking with FTDI.

Cluso99

Here is another thread http://forums.parallax.com/showthread.php?133362-Why-do-we-need-the-transistor-reset-circuit-for-the-USB-devices-(FT232RL-CP2102)&highlight=usb+ttl+cp2102

I would however use the full transistor circuit (at least provide the circuit for it on your pcb just in case) because the capacitor may not work in all circumstances.

The CP2102 is only available in QFN which is very difficult to hand solder. Many find the FT232RL difficult enough to hand solder although I have not found any problems.

To get to the heart of your question, the FTDI chip is not much different in price to the CP2102 in low quantities so it comes down to space. As Mike said, the FTDI chip has been proven to work reliably over time whereas the other chips have had a very checkered history. The circuit of the FT232RL is similar to the CP2102 and is definately no more complicated. My research over the past few weeks meant I concluded that I would continue to use the FTDI chip.

Have you layed out pcbs before, and do you have the ability for soldering the QFN chip? IMHO... If so, then the CP2102 will probably work fine for you. If not, go the safer route and use the FT232RL.

Thric

Thanks for the suggestion. I've laid a few PCBs out before with no problem and dealt with QFN packages, i find that by just extending the pads a little you can easily drag solder with a normal hand soldering tool. But hopefully i can get some acess to a rework station.
Thanks for all the help.
~Osi