Hi everyone,

My problem is quite difficult to understand.
I'm using a PIC burner that works with RS-232 lines (Vpp:TX, write dataTR, read data from PIC:CTS, clock:RTS). This is a really simple circuit that involves few parts (NPN, PNP, Max232, CD4049). The software used to burn the PIC is WinPic800 v3.59

It works fine on desktop computers (Windows 98, XP). But it doesn't work on my Compaq laptop (Armada E500, Windows 98). I guess that baud rate, stop bits etc, are not involved in the serial comm. because the USART is used differently. This is not a standrad RS232 comm. So, it seems to be a driver problem (related to hardware). Does anyone can give me some hints?

Mike

 

The output voltage of the RS-232 signals on some laptop personal computers is well below RS-232
standard levels. Charging the batteries or connecting the personal computer to AC power will
sometimes help.

 

IIRC, sometimes laptop ports don't have the same current capacity as those in a desktop (where power consumption is immaterial). I remember when parallel port keys for copy protection were popular and many people had problems with them when used on laptops.

--
Steve Myres, PE
Automation Solutions
(480) 813-1145

 

Some laptop "serial" ports are not actually RS-232. They use a lower signal voltage to reduce components (e.g. charge pumps, etc.). Some devices expect to see standard RS-232 voltages, and won't work with the non-standard (low voltage) ones.

 

Depending on the PIC, it may need up to 13 odd volts to program. If using a straight RS-232 connection, you are relying on the port putting out sufficient volts to meet this requirement. Your laptop RS-232 may not be putting out that much - many work at the low end of the RS-232 voltage window.

 

Since everyone seems to agree that signal levels from laptop ports are the issue, maybe something that uses an external power source, like a 232-232 isolator from Black Box, or something like that, would resolve the issue, as long as it would read the low level signals from the laptop.