CommPort Test In V 6.0.8.0

CDRIVE

Senior Member
I'm curious.. I only have USB ports on my PC, so the prompt screens seen throughout the COM port - Configure & Test wizard are what I'd expect to see, including the voltage test (0V & 5V) using the active "Click LED" window. My question is if I had a real Serial Port and selected it in the first window's drop-down would the Voltage Test prompt screen (Click LED) display RS232 voltages ... -12V & +12V?

I'm asking this because a friend says he's seeing screen prompts returning USB/Serial converter levels of 0V & 5V when clicking the LED even though he's using a real Serial Port. His measured voltages are what they should be though.

Thanks.
 

hippy

Technical Support
Staff member
It depends on where the voltage is measured.

A real RS232 cable measured before the download 10K/22K interface may well show -12V/+12V.

After the interface, measured on the PICAXE Download Serial In pin, the voltages should be 0V/5V or thereabouts. Internal diodes of the PICAXE clamp the voltage close to 0V and 5V.
 

CDRIVE

Senior Member
It depends on where the voltage is measured.

A real RS232 cable measured before the download 10K/22K interface may well show -12V/+12V.

After the interface, measured on the PICAXE Download Serial In pin, the voltages should be 0V/5V or thereabouts. Internal diodes of the PICAXE clamp the voltage close to 0V and 5V.
Yes I understand that but that was not my question. My friend is doing his measurements at the mini plug end of the cable, not connected to the Picaxe resistive network. IE, as shown on the Picaxe prompt screens. I would fully expect that he's reading ~-12V & +12V, as this is normal RS232 levels. My question is not about what he measures but rather the Picaxe prompt screens. I would think that the voltmeter 'graphic' would not display 0-5V as he's seeing but rather -12V (LED OFF) and +12V (LED ON). As I said I don't have a Serial Port so I can't duplicate the Picaxe prompts and returns that he sees. Are you saying that the LCD voltmeter graphic doesn't vary depending on whether it's an RS232 port or a USB/RS232 converter like the Axe027?

I hope I'm making myself clear. If not I'll attempt to restate it yet again.
Thanks.
 

hippy

Technical Support
Staff member
Sorry; I did not read the question accurately. My understanding is the test program would only show "0V/5V" as screen displays and in graphics as it would not know what type of cable is being used, what voltage output it generated.

However, it probably was different in the past, before the AXE027 USB cables, and there may be differences between test programs and different PICAXE software.
 

CDRIVE

Senior Member
Sorry; I did not read the question accurately. My understanding is the test program would only show "0V/5V" as screen displays and in graphics as it would not know what type of cable is being used, what voltage output it generated.

However, it probably was different in the past, before the AXE027 USB cables, and there may be differences between test programs and different PICAXE software.
Speaking strictly of V6.0.8.0 I find your reply rather odd to say the least. After all the CommPort Test Wizard steps the user through procedure screens. One of which prompts the user to "Select the COM port for the download cable". This screen includes a ListBox - Drop-Down (if any) of all recognized serial ports, virtual or physical. It's only logical that if the user has and selects a physical serial port the wizard would then know it's a real serial port. Subsequent wizard screens should then be formatted to reflect the voltages expected for a physical serial port.

I must say that I'm astounded that I'm apparently the only member that has questioned this. Please pass this discrepancy along to the software development team. Heck, it would take only a few lines of If - Then code to remedy this issue.

Thank you very much for your knowledgeable input.
 

techElder

Well-known member
... I must say that I'm astounded that I'm apparently the only member that has questioned this....
Probably because when we download a program, we also test the comm port etc. There aren't a lot of choices involved with repairing a connection, so using a "wizard" doesn't really add much to the game.

In my case, anyway. Your mileage may vary.
 

CDRIVE

Senior Member
Probably because when we download a program, we also test the comm port etc. There aren't a lot of choices involved with repairing a connection, so using a "wizard" doesn't really add much to the game.

In my case, anyway. Your mileage may vary.
One of the things that I did during my long electronics career was teach for a few years. Students will get confused on their own without being compounded by external influence. My friend is a nube and was very confused by the wizard's screen returns. I think he should have been and I also think this should be corrected. ;)
 

hippy

Technical Support
Staff member
After all the CommPort Test Wizard steps the user through procedure screens. One of which prompts the user to "Select the COM port for the download cable". This screen includes a ListBox - Drop-Down (if any) of all recognized serial ports, virtual or physical. It's only logical that if the user has and selects a physical serial port the wizard would then know it's a real serial port.
The problem is that the Wizard asks Windows for a list of serial ports and their names and is given those and displays them. But there is no specific information returned as to which may be physical ports and which may be USB, URF or other virtual ports.

While some names may give a fair indication as to what they actually are , the names given to various ports can change depending on OS, device driver installed, and can always be changed by the user.

The actual voltages put out by the hardware is unknown, even to Windows. Anything between -/+3V and -/+25V can be expected for RS232, and nor would it be known if a particular USB cable put out one of those voltages or 0V/5V. Even some physical serial ports, particularly laptops, can put out 0V/5V.

The bottom line is that it is not possible to tell what voltages may be put out by any particular serial port. While it can be guessed at there is no guarantee that the guess would be correct.
 

CDRIVE

Senior Member
Hi Hippy,

Sorry for the long delay in responding to your last post and thank you for the clarification.

Chris
 
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