I have my modem installed as /dev/ttySL0

If I do stty:

parkinson@punkd# stty -F /dev/ttySL0 -a
speed 9600 baud; rows 0; columns 0; line = 0;
intr = <undef>; quit = <undef>; erase = <undef>; kill = <undef>; eof = <undef>;
eol = <undef>; eol2 = <undef>; start = <undef>; stop = <undef>; susp = <undef>;
rprnt = <undef>; werase = <undef>; lnext = <undef>; flush = <undef>;
min = 5; time = 0;
-parenb -parodd cs8 -hupcl -cstopb cread clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl ixon ixoff
-iuclc -ixany -imaxbel
-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
ff0
-isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase -tostop
-echoprt -echoctl -echoke

but, if setserial

parkins@punkd# setserial -a /dev/ttySL0
parkins@punkd# Cannot get serial info: Invalid argument

What could be the reason for the setserial response?

Thanks