Minicom cant get info from /dev/ttyS0 and ttyS1

I try to get serial communication with a broadbandrouter
When i use PCPLUS with DOS 5.0 i can get communication
with the router (115200 N81 No Software Control / No hardware Control)
It works both on comm1 and comm2

If i try to communicated from Fedora 6 with minicom
I get for ttyS1 --> device does not exist
for ttyS0 --> i get nothing

If i look at the /dev directory i see the devices ttyS0 to ttyS3
(with dev ttyS0 connected)

crw-rw---- 1 root uucp 4, 64 mrt 28 15:24 ttyS0
crw-rw---- 1 root root  4, 65 mrt 28 2007 ttyS1
crw-rw---- 1 root root  4, 66 mrt 28 2007 ttyS2
crw-rw---- 1 root root  4, 67 mrt 28 2007 ttyS3


Where do i have to look, to make the serial connection work on comm1
(ttyS0).

Thanks

Erik