Technical,
You must forgive me for my out burst due to frustation, this has been an ongoing problem with the 20x2 ever since it was released, and up to now it would appear the problem has been swept under the carpet, good to see you are finally stepping up to resolving the problem.
Lets face it, as far as i have tested with the current chip range (and not used all the range as yet) this is the only chip with a serial problem, making it a lemon to the rest of the range, over all its the best chip in the range if the serial problem is fixed.
To answer your questions, and granted there is more information you should have that i have not supplied (more so didnt consider it required) due to the fact all other chips work with hardware or software used within the chip and external programs communicating via serial coms.
The first time i suggested a serial problem with the 20x2 it was implied because i was not using a Rev-ed approved Usb to serial adapter (being the one rev-ed sold) then the problem was my serial cable of choice used........ Rubbish!!!
If a cable work faultlessly with every other chip range in picaxe or other serial chips, then the problem is within the chip (20x2)
For the sake of the problem lets except all other picaxe chips operate as expected with software , hardware, serial adapters used, where the 20x2 wont, this quickly eliminates serial problems due to 3rd party software, hardware design, and code used, and serial interface type (various Usb to serial adapters)
If a direct serial cable between picaxe and PC is used, the calibfreq is not always required, but as soon as a USB adapter is used (commonly the blue/green Chinese Usb to serial cable adapters, but no limited to these) the need to adjust internal clock is required to enable "sertxt and serrxd" to operate without corrupt data being received.
( i expect now the problem becomes the method of serial coms used and not a firmware problem........ rubbish!!)
From what i am seeing the use of calibfreq then effects the commands of "Serin/serout" rendering the chip useless when depended on as various methods of serial communications.
I will assemble some basic test code that reflects the code used and supply to you , but unless you put the view of the Rev-ed usb adapter is the only coms link you are prepared to test with to one side, then the problem may never be solved.
It is not as though i am some school kid with a project problem, and wish to blame the picaxe chip, its a long on going problem that just gets worst with the 20x2 and serial coms with every time i have used it, the unfortunate part is i used the chip in several circuits that use serial coms, and once there is more than one chip involved the problem becomes double, with one chip talking Chinese and the other Japanese creating a lot of noise but no communication between chips.
First up, can you purchase one of these cables, as they are compatible with the effects of every other USB adapter i have ever used with the picaxe here, and then test with this cable, as the result here fits all adapter types i have used.
Surely Rev-ed can afford the $3.00 for the cable in the name of research, as half the picaxe users work with them.
(if not let me know and i will purchase the cable and have it shipped to you)
http://www.ebay.com.au/itm/250512172218?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
Once you have the adapter cable and run a few tests, also try receiving data into a VB program and see if you get 100% data, from what i have seen just because the terminal window receives the data, it dont always mean other standard serial protocol programs will work without adjusting the calibfreq for "sertxd and serrxd"
Im sure by now there will be a witch hunt to prove me wrong, but the fact is, there is serial issues with the 20x2 and without some attention the problem will always exist.
Perhaps i do things with other software interfaces and inter serial links that most other users dont do on the average, but it still dont solve the 20x2 problems.
Give me a few days to sort out some simple test code, and i would like to setup and test the code examples here first so we are all on the same page. Its been a few years in the problem so a few days should not matter, as well it will take that long to receive the Usb adapter cable requested.