my %registers = %{$d->{regs}->{r}};
foreach my $reg (keys %registers){
  my $reg_id  = hex $reg;
  my $reg_num = $registers{$reg};

  # read_input_registers returns an array reference
  my $tmp = $mbc->read_input_registers($reg_id, $reg_num);

  $r->{$reg} = _prettify_byte($tmp);
};