warn "<< ", as_hex($r_len,$data),
' | ',
substr($data,-2,2) eq checksum(substr($r_len,1).substr($data,0,-2)) ? 'OK' : 'ERROR',
warn "<< ", as_hex($r_len,$data),
' | ',
substr($data,-2,2) eq checksum(substr($r_len,1).substr($data,0,-2)) ? 'OK' : 'ERROR',