RS-232 to Propeller

O.A.A.

Using "Serial to Propeller" circuit given in Propeller Diagrams,Schematics, and Images I have no problem programing the Propeller chip using the standard serial port of my PC. However, when I connect it to the standard serial port of my laptop I get the error message: "No Propeller chip found on any serial ports". Any suggestions on what might be happening?

Peter Jakacki

Most laptops don't have serial ports but I have seen some brands of laptops that do have standard serial ports behave in a weird manner. It seems that when the port is not "opened" that it exhibits something akin to sending a continuous break condition plus it is quite possible that the handshake lines are also affected. I had no end of problems with one customer's brand of laptop until we figured out what was going on.

Check your outputs from the laptop with a multimeter to make sure that it behaves correctly both when the port is closed and when it is opened. You can open the port normally by running Hyperterminal to check it's operation. Also a simple loopback can be used as well to test the hardware. Laptop serial ports are also prone to damage, especially when the laptop is running from mains power as they are not isolated. This could be your problem.

*Peter*

CannibalRobotics

Does the port respond properly to other serial devices?

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O.A.A.

Yes, the port responds properly to other serial devices. No problem in programing Basic Stamp chips. Laptop is Dell Latitude D505.
O.A.A

RiJoRi

I had a similar problem with an AVR Butterfly. I needed to connect the hardware pins together (I think it was 6, 8, and 23?* ) before the serial comms would work -- didn't matter what I told the comm software about ignoring hardware handshaking: the port was too smart for my own good! Also, there was a time I tried opening a port that another software package had opened, and it took some time before I realized what had happened. There was no "Port in use" message, just an unhelpful "No device found" message.

--Rich
* I'm at work, so this is from memory, and it applies to the DB-25 connector. Do a Google search for Null Modem Cables.

O.A.A.

Thank you Rich. Your note made me remember that in all Basic Stamp schematics it is stated to connect DSR and RTS pins (pin 6 and 7 for DB9) for automatic port detection. I did this, but unfortunately it did not solve the problem. Nothing changed.
O.A.A.

StefanL38

Hello O.A.A.

there is a trouble-shouting guide about this issue that you can download from parallax.

Did you do all the things mentioned there ?

best regards

Stefan

O.A.A.

Thank you for your note Stefan. No, I didn't know of such a guide. I did a search of the Downloads page on Propeller Articles, Software and Documentation but could not locate a related topic. Could you please give the page address.
Thank you.

StefanL38

Hello O.A.A.,

USBDriverTroubleshooting-V1.0

best regards

Stefan

O.A.A.

Hello All,
I have reduced the latency timer setting from 16 to 1. Nothing changed.
I'll summarize the the problem again :
1. I have a PC and a laptop both with standart serial ports.
2. I am using the 3 transistor circuit given in Propeller Diagrams, Schematics and images.
(The DRS and RTS pins shoted.)
3. I have no problem in connecting and downloading from PC.
4. When trying to connect to the standart serial port of the laptop propeller chip is not recognized.
Reducing latency timer settings made no difference.
The port responds properly to other serial devices. No problem in downloading to BS2 chips
using Max232 serial interface. Seems 3.3v is behind this somehow.
Thank you all.
O.A.A.

Andrew E Mileski

You should check the voltage on the DTR pin.

DTR is normally asserted (logic 0 = +3 to +25 Volts), but the simple transistor Propeller interface requires it to be negated (logic 1 = -3 to -25 Volts).

It is possible that your laptop has DTR permanently asserted, as this saves a level shifter. Typically there is only support for RXD, TXD, RTS, and CTS. RTS can be substituted for DTR if the software also negates it and uses it for reset.

Post Edited (Andrew E Mileski) : 12/8/2008 10:20:06 PM GMT

mikediv

heres a thought did you go into the control panel on your laptop , device manager then select seril port and then setting you will see somehting like n,8,1 19200 baud rate hardware control , change it to n,8,1 baud rate 9600 and NO FLOW control
that should do it I have the same laptop the prop seril port didnt like having the RS-232 port set to hardware control just change it to none hope that helps I built same circuit and just used 2,3 and 5 ground pin make sure you switch 2 and 3 I had to

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O.A.A.

Hello,
I am back again. I did everything suggested but it made no difference. As I mentioned last time, I had a suspicion that somehow the 3.3v circuit may be behind this problem. Well, changing to a 5v max232 circuit (with a 1k resistor on Rx pin of prop) solved the problem. Thanks to all replies.
O.A.A.

O.A.A.

Hello,
I am back again. I did everything suggested but it made no difference. As I mentioned last time, I had a suspicion that somehow the 3.3v circuit may be behind this problem. Well, changing to a 5v max232 circuit (with a 1k resistor on Rx pin of prop) solved the problem. Thanks to all replies.
O.A.A.

warner

If your using the PropStick USB you have you have to install the USB driver on the laptop.