Reusing my FT232R cable

oscarc

Hi all,

I am a programmer, not an electornic engineer so i have a very basic question that haven't solve even browsing the sticky threads.

When i was using TTL microcontrollers i purchased some USB to TTL (5v) serial cables form FTDI: http://www.ftdichip.com/Images/ttl232rsch1.jpg

Now i have purchased some P8X32A-40 to experiment with spin and i have no idea on how to reuse·the cables with the propeller.

The connections could be:
·······················
Cable RxD

---

10K--- P30
Cable TxD

---

P31

I put a 10K R· on the RxD (for TTL to CMOS) althought·the cable schematic have already one on RxD and other on TxD.

Then for the DTR:

Cable RTS# ---10nF---10K Pull down---NPN---ResetToGround--- RESn

Is this correct?

Thanks in advance?

oscarc

Hello again,

Please, i only need a little help. Could some one tell me if this schemtic (in the attachment) is valid to avoid frying my first propeller micro.

Thanks.

Ariba

No your circuit is not correct. The seriell resistor has to be between TXD and Pin31 to protect from the 5V Level from TXD.
Look at the attached GIF for a better schematic. I use such a circuit one year now, without problems.

Andy

Edit: If you can then use DTR instead of RTS, but the IDE can also handle the RTS to produce a Reset.

Post Edited (Ariba) : 4/10/2008 11:01:50 PM GMT

hippy

Ariba said...
No your circuit is not correct. The seriell resistor has to be between TXD and Pin31 to protect from the 5V Level from TXD.

I always try to explicitly indicate where a TX or RX is to or from to avoid such ambiguities.

oscarc

Ariba said...
No your circuit is not correct. The seriell resistor has to be between TXD and Pin31 to protect from the 5V Level from TXD.
Look at the attached GIF for a better schematic. I use such a circuit one year now, without problems.

Andy

Edit: If you can then use DTR instead of RTS, but the IDE can also handle the RTS to produce a Reset.

Hi Andy.

First of all thaks a lot!

I have several prebuilt cables from FTDI with only TXD, RXD, CTS and RTS signals, so i can't use DTR for the reset.·I will place a switch between RTS and reset to avoid posible comunication problems in normal operation.

My·last doubt now: as in your schematic, no need of using·a serial resistor for RTS, right?

Oscar
·

Ariba

oscarc said...

My last doubt now: as in your schematic, no need of using a serial resistor for RTS, right?
Oscar

Right!
If the Transistor gets a 3.3V puls or a 5V puls does not matter for the Propeller.

But if you mean your 10k resistor between the NPN and the Reset: This will not work. The Reset Input has an internal PullUp with ~ 5 kOhm, so a 10k to Ground will never produce a Reset. A 1kOhm will most likely work, to play it save. And then you can also add a seriell resistor in the RXD line (1...4.7k). But both is not really necessary.

Andy

oscarc

Ariba said...

oscarc said...

My last doubt now: as in your schematic, no need of using a serial resistor for RTS, right?
Oscar

Right!
If the Transistor gets a 3.3V puls or a 5V puls does not matter for the Propeller.

But if you mean your 10k resistor between the NPN and the Reset: This will not work. The Reset Input has an internal PullUp with ~ 5 kOhm, so a 10k to Ground will never produce a Reset. A 1kOhm will most likely work, to play it save. And then you can also add a seriell resistor in the RXD line (1...4.7k). But both is not really necessary.

Andy

Thanks again, Andy.
All is clear now. I will try it on the protoboard this afternoon and, with luck, run my first spin code.

Ariba

Don't forget to connect BOEn to Ground, only then the internal Reset-PullUp resistor is enabled.

Good luck