Perhaps the punctuation characters on your keyboard are broken. 😒

What have you plugged your "gm300" into? Do you have a COM1 listed in your Device Manager? Are you using a USB-to-RS232 cable of some sort?

In any case, programming stuff over the serial port is beyond the scope of DOSBox and it may be impossible to get it working.

thanks triple checked punctuation setup com1 in device manager I'm plugged into rib box that I used with and old laptop I no longer have
Jeff

Perhaps I was being too subtle. Let me try that again: your posts are very hard to read when you do not use punctuation.

If you have COM1 in Device Manager, but DOSBox tells you COM1 does not exist, then I really don't know what to tell you. There may be something seriously wrong with your system. The only other thing you might try is to run DOSBox as an Administrator.