Variations in computers' DCE-DTE?
BillNorman
Posts: 1
The company that I work for as an engineer uses a BS2SX in their previous products (meaning those that were not designed by me, further meaning that I am not very familiar with the Stamp and its environment).· I have been seeing a certain inconsistency in the operation from host to host.· The firmware in·our company's·original product allows for simple configuration of the device (using HyperTerminal) through the Stamp's primary serial port -- the same port that is used for programming the Stamp.· Using a null modem cable attached to the host computer, all has been hunky-dory for years.
All of a sudden (well, like within the last year or so), we have begun to see some discrepancies in the operation from one host computer to the next.· It seems to primarily happen with laptops, specifically newer Dell laptops.· Whereas we have been using null modem cables on desktop computers for so long without any issues, we are now finding that the null modem cables on newer laptops don't work, and require another null modem adaptor - essentially making the complete connection a straight-through.
So I am wondering if there is something in newer computer configurations that somehow make the computer's serial port changeable·between DCE·and DTE, and if there is a way in the computer's control panel to change this?· Or is there something about HyperTerminal's operation on these computers that causes this situation?· So far I have found nothing, but I can't explain why it would be different on different computers.
If this question has been addressed in a previous post, my apologies.· It's difficult to make myself browse through over 4000 forum topics.
Thanks loads for any light that might be shed on my feeble existence.
Bill
·
All of a sudden (well, like within the last year or so), we have begun to see some discrepancies in the operation from one host computer to the next.· It seems to primarily happen with laptops, specifically newer Dell laptops.· Whereas we have been using null modem cables on desktop computers for so long without any issues, we are now finding that the null modem cables on newer laptops don't work, and require another null modem adaptor - essentially making the complete connection a straight-through.
So I am wondering if there is something in newer computer configurations that somehow make the computer's serial port changeable·between DCE·and DTE, and if there is a way in the computer's control panel to change this?· Or is there something about HyperTerminal's operation on these computers that causes this situation?· So far I have found nothing, but I can't explain why it would be different on different computers.
If this question has been addressed in a previous post, my apologies.· It's difficult to make myself browse through over 4000 forum topics.
Thanks loads for any light that might be shed on my feeble existence.
Bill
·
Comments
As far as I know, the programming port on a BOE board is designed to NOT need a 'null-modem'. Now, if you're using a 'home-grown' board solution, it sounds like the creator of that intended you to use a null-modem adapter to connect a PC to the port. If somebody has changed how they wire that 'home-grown' port, that could explain the differences you are seeing.
The short answer is NO, there is really no way to change a DB-9 port from DCE to DTE type through software. We're talking moving a driver to a reciever, and a reciever to a driver. Those are hardware mods, or pin changes. And as far as I know ALL PC serial ports are wired DTE, intended to connect directly to a Modem wired DCE.
So it sounds like there's some change in how your boxes are being made, quite frankly.
If you really want to get away from the differences in manufacture between laptop vendors, you could easily use a USB to serial adapter, like the FTDI unit offered by Parallax. Stay away from Belkin, or any marked "for PDA's", as these adapters typically don't properly implement the 'hand-shake' signals needed to reset the BS2.
Oh, and you should note that the way I get around these "mystery RS232 configuration" issues is with a simple 8-LED RS-232 monitor box from Radio-Shack.· This will immediatly show if you've got TX connected to TX, or two TX-RX links properly connected.
I think the previous poster has hit the high points on how to fix the problem.
Computers are in general DTE devices with male 9-pin connectors. Female connectors should be DCE in order to stick with straight-through serial cables.
Early on, we also had similar issues with the BS2 serial connections. It stems mostly due to there being a resistor connecting the TX and RX circuits deep within the hardware of the Stamps. There are valid technical reasons for it. But, in testing, particularly with a strong RS232 port on a laptop, it can appear that the Stamp can read the serial string regardless of whether you connect the laptop data-out to pin 2 or 3 on the Stamp.
Once we looked closely at the module schematics and traced things back to the Stamp module Sin and Sout, things got sorted out and we've standardized ever since.
Regards