The 0.1uF capacitors when using FTDI programmer

Vincent19:
Why not ? My ftdi programmer have the DTR pins and I am required yo connect it to reset pins via 0.1uF cap..but I do not know why

Your ftdi programmer connects to the reset pin. With serial you have no connection to the reset so the designers of the arduino decided to use the handshaking pin as a reset, rather clever I thought.

RTS goes low, as shown here:

However we don't want reset to stay low, so the capacitor turns it into a pulse. Then 10K resistor then charges the cap back up and it becomes high, allowing the processor to run.

And that is why a wise person said "a picture is worth a thousand words".

Lefty

Does that means that I only have to connect RX, TX , gnd and vcc to MCU?

Depends if you want auto-reset or not.

If I never connect the DTR pins, I still can load my program to chip using ftdi programmer ?

If you don't connect the DTR/RTS via the capacitor you will have to manually reset the chip at the same time you upload a new sketch.

But the timing has to be right, hold down the reset, select the program from the IDE, when it says loading, count one two three, and release the reset.

on this link it shows the reset to reset connected with a cap in between and no mention of DTR CTS etc

http://openmicros.org/index.php/articles/88-ciseco-product-documentation/124-xb4a-how-to-build-arduino-compatible

why is that different ??

knuckles:
on this link it shows the reset to reset connected with a cap in between and no mention of DTR CTS etc

http://openmicros.org/index.php/articles/88-ciseco-product-documentation/124-xb4a-how-to-build-arduino-compatible

why is that different ??

Simply a misprint on that site's pin out of the 6 pin FTDI pin out, where it says RST it should say RTS. Either the RTS or the DTR signal can be used to generate the auto reset pulse, as the arduino IDE uses both.

Lefty

Grumpy_Mike:
But the timing has to be right, hold down the reset, select the program from the IDE, when it says loading, count one two three, and release the reset.

Great info!!! Will have try it . And let you know soon !

Thanks :slight_smile:

dtr is preferred over rts because its much better behaved under windows.

Great ! How about CTS? What's that ?

Vincent19:
Great ! How about CTS? What's that ?

Not required in this application and can be left disconnected.

Lefty

When will CTS being used ?

If the PC com link was set-up with the 'hardware handshacking' enabled, the CTS (clear to send) would be how the device would tell the PC it was ready to receive data if any is waiting to be sent. The comm port as used by arduino (and most all PC serial applications) use the 'no handshake' option choice to run the link at. There is also a 'software handshake' option where the two sides of a comm link send the ascii Xon and Xoff control characters to tell the other side to stop or start sending data. That is also not used in most PC applications. But both options are available for interfacing with such thing a older modems and other data communication devices.

Lefty

Vincent19:
Great ! How about CTS? What's that ?

cts, dsr, ri, etc are inputs to the pc and therefor can never be used as arduino control bits.

Grumpy_Mike:
But the timing has to be right, hold down the reset, select the program from the IDE, when it says loading, count one two three, and release the reset.

I have tried this ! It's really do work well ! But the timing really have to be correct. Have to release the RESET button once the IDE shows 'uploading..'

Thanks ! Finally I understand why is there a cap there- to bring the RESET High and LOW. :slight_smile:

When I want to upload a new sketch, the we should RESET our microcontroller so that the previous sketch is deleted and pull the RESET HIGH to allow the new program to load into ?

Am I correct ?

Thanks !

Thanks ! Finally I understand why is there a cap there- to bring the RESET High and LOW.

Well actually that should read 'to bring the reset Low then High'. :wink:

Lefty

Resetting the processor does not delete the old sketch.