Often I am asked various questions about the Serial port on different OS'es and compilers. And thought this the most appropriate forum to answer the various people involved.

Question:
Here is the background: when I run the PBCC 5.0 sample communications program and comm.bas, I can only open COM3. The 64-bit Vista OS does not even seem to offer the serial communications options that other Windows operating systems had.
Tests: (Most cases, should not matter the OS nor the compiler)
  1. Running my own program written in PbWin that scans from Com1 to Com9 (easily changed for Com above 9).
  2. Look in the device manager under "Ports Com and LPT" for a list of ports that exist

User Replies:
  1. The COSMOS software scanned 9 ports. Except for COM3, all ports were closed. The message said that there was an application running on each of the closed ports.
  2. Vista does not offer the com port parameters in the device manager.
Results: (Or my thoughts as to real results)
  1. Shows that Com3 is available, but the reason that status showed "there was an application running on each of the closed ports." is that those ports do not exist as far as Windows is concerned (Same error as if port existed, but another program/driver already has the port)
  2. Vista does offer the com port parameters in the device manager, but like other OS'es that there are no LPT nor Com Ports, then the category itself does not show up. (Odd though that COM3 would open and not exist in the Device Manager, but more on that later as to what I think it is)
Question:
How do, or can you, select and modify com port parameters with <Insert OS Here>?
Results: (Or my thoughts as to real results)
  1. Comm.bas is a real good starting point (Take a look at the "COMM SET" for a PB way, or if really ambitious the same with the WinApi)
Question:
Can you have multiple com ports open with <Insert OS Here>?
Results: (Or my thoughts as to real results)
  1. Yes, but that answer is more "It Depends" because it can get really hairy if you do not code it just right, and can be realy hard to debug. But yes it can be done.
Question:
I can see what I send/recieve to the serial port, but the transmit/recieve characters are all garbled
Results: (Or my thoughts as to real results)
The reason could be one of the following: (if not more)
  1. The function sending/recieving the commands could be expecting one type and what is passed is another type (typical String vs Asciiz vs Pointer to String vs Pointer to actual String data
  2. Could be communicating at the wrong baud rate, or other parameters
  3. Device being communicated with could be set to different Baud rate, or other parameters
  4. The characters are seeing are certain characters in the ASCII set of 128 to 255
Question:
I open COM1 as seen in the example, but I can not communicate
Results: (Or my thoughts as to real results)
The reason could be one of the following: (if not more)
  1. Com1 is just a default for starters, and may already be used by another program, or driver, or firewall, or something else like there is no COM1
  2. Could be communicating at the wrong baud rate, or other parameters
  3. Device being communicated with could be set to different Baud rate, or other parameters
  4. You could be communicating and not know it, if the characters are unprintable (certain characters in the ASCII set of 128 to 255)
More questions, and avenues to research as time lets on