readbyte
readbyte ( )
readbyte ( open_file_number )

returns integer_expression

Reads and returns the next byte (8 bits) as a number 0-255 from an open file. If the file number is not specified file number zero (0) will be used.
File should be opened with the Openb statement so that ASCII CR/LF translation does not happen.
In you are reading a serial port opened with OpenSerial no translation will happen. Additionally a -1 will be returned if there was no data in the receive buffer.

cls
f$ = "binary.dat"

print "new file"
openb f$
reset
for t = 1 to 20
   n = r()
   print n+" ";
   writebyte n
next t
print
close

print "open and read"
openb f$
while not eof
   print readbyte()+" ";
end while
print

print "position to 10 and read"
seek 10
while not eof
   print readbyte()+" ";
end while
print

close

end

function r()
   r = int(rand*256)
end function

will display something like

new file
181 163 155 23 46 93 122 212 178 225 1 62 113 130 202 52 185 51 37 165 
open and read
181 163 155 23 46 93 122 212 178 225 1 62 113 130 202 52 185 51 37 165 
position to 10 and read
1 62 113 130 202 52 185 51 37 165