RS232 on laptop and

[Gon]

Hello,

i have a little problem with RS232 on 2 computers :

When i try to get some ascii characters on a laptop with the serial port monitor, my PIC18F458 gets them with no problem with getc() function.

But when i try to do exactly the same thing but with my PC, it is not working at all...

Is there something that must be done for my PC to work like the laptop ?
Is there a difference of voltage level or something pretty much like this between these two computers?

Please let me know.

Many thanks.

Best regards.

[Ttelmah]

Are you sure you are talking to the right port on the PC?. Normally the problem tends to be the other way round, with laptop serial ports often tending to use slightly 'sub standard' voltages, and having an extra 'invisible' port at COM1, which drives the infra red communications, rather than a real port.
Disconnect your PIC circuit, and connect pin 2 on the PC com port, back to pin 3. This 'loops' the transmitted data back to the receive line. If you send with echo turned on, you should see every character appear twice, or if you send with echo turned off, you should see the characters once.
Check in control panel, that handshaking for the port is set to 'disabled', or 'XON/XOFF'. If this is not done, the port may be waiting to see an external handshake signal, that is not there.

Best Wishes

[Gon]

Everything is ok with the COM1 beacuse i only have one port on my PC, really similar to a laptop that has only one serial port which is COM1.

[rberek]

Assuming WindowsXP:

Start -> Control Panel -> System -> Hardware -> Device Manager -> Ports

Right click COM1 and select the Settings tab.

If you have an older version, it may be Start -> Settings -> Control Panel ...
_________________
The difference between genius and stupidity is that genius has its limits...

[Gon]

Hello,
thanks for help.

Still not working ...
Any other suggestion ?

[Ttelmah]

What is actually shown under the ports tab in control panel?. If it shows more than one com port, it may well be that your motherboard actually has two ports, but only one has an external connector!...
To change the handshake, double click on the port, then select 'port settings'. At the bottom of the entry list here, there is the handshake setting. Also below it, is a tab 'advanceddddd', and if you select this, you can set the actual port 'name' to be used.

Best Wishes

[rberek]

In the Device Manager, was there a yellow circle with an exclamaton point in it over the COM1 line? This indicates that there is a problem with it.

Is the COM1 port enabled?

Have you ever used the COM1 port on your PC before for other things?

Is the COM1 port on a PCI serial port card rather than the motherboard itself? If it is a really new PC, the motherboard may not have a serial port connector and the serial port is provided by a plug in PCI card. I have had problems with this in the past.
_________________
The difference between genius and stupidity is that genius has its limits...

[Gon]

There is only one port COM on this motherboard.
There is no Exclamation point in the device manager.
I use the COM1 with the bootloader TinyBootloader with no problem to update the software, i can see what is coming from the PIC with the serial port monitor, but i can't 'send' any ascii character. The PIc doesn't 'see' any character sent.
There is only one other port which is the parallel port and is not used.

I tried Xon/Xoff and disabled for settings but still not working.

I suppose it should be a hardware feature but how could you explain that with a laptop there is no problem but with my PC, it is not working ...

[Ttelmah]

How is the circuit wired.
The obvious difference between the laptop, and the desktop PC, is that the latter, generally will have the case grounded, while the laptop will 'float', providing full isolation. You may have a problem, depending on how your PIC circuit is powered/connected.

Best Wishes

[Gon]

I don't really know what i can even do, because the circuit is wired as you mentionned before, on pins 2 and 3.

I have the ground which is on pin 5.
Do you think the serial port cable (which is different for the desktop computer cable and for the laptop) could be a problem ?

They are 2 different cables but they look the same ...

[rberek]

I would try the cable you used with your laptop on your PC. There is a chance the other cable is broken or is a null modem cable.
_________________
The difference between genius and stupidity is that genius has its limits...

[Gon]

Ok,
i'll try then but i am not that sure that this would solve my problem.
If any other idea comes to your mind, let me know about it.

Many thanks anyway !

[Ttelmah]

[arunb]

Hi,

The voltage level on a PC is +/- 12 and on the laptop it is +/- 5 V.

thanks
arunb

[Ttelmah]