I need some expert help, please.
The following is all the info I can find on TOBYTE

:run help.hpbin.sys;info="tobyte"

tobyte -- convert MPE record files to byte stream files
Usage:  tobyte [-at] mpe_file [hfs_filename]
-a      open the input file as an ASCII file
-t      strip trailing blanks from each line in an ASCII file

but when I try the above syntax (whether or not including -at)

:tobyte.hpbin.sys test2 test3
                        ^
Expected a comma or a semicolon. (CIERR 10125)
Implied run command failed due to parser error. (CIERR 9057)

with the ^ pointing to the second filename.

Putting a comma between the filenames results in

An integer value between -2147483648 and 2147483647 expected. (CIERR 10010)
Implied run command failed due to parser error. (CIERR 9057)

Putting a semi-colon between the filenames results in

This is not a valid option for this command. (CIERR 10006)
Implied run command failed due to parser error. (CIERR 9057)

What am I doing wrong? I've tried just about everything, including running from the shell. But I obviously haven't found the secret.

Help, and thanks.

Shirl, (Crossley Carpet Mills, Truro, NS)