try stuff?

 
modpoll
-b 4800 #          Baudrate
-p none #          No parity
-a 1 #          Slave address (1-255 for serial, 0-255 for TCP, 1 is d
+efault

-r 13 #          Start reference (1-65536, 1 is default)
-c 1 #          Number of values to read (1-125, 1 is default), option
+al for writ
ing (use -c 1 to force FC5 or FC6)
/dev/ttyUSB0
[download]

so

my $client = Device::Modbus::RTU::Client->new(
    port     => '/dev/ttyUSB0',
    baudrate => 4800,
    parity   => 'none',
);
 
my $req = $client->read_holding_registers(
    address  => 1, # -r
    quantity => 1, #-c
);
 
$client->send_request($req);
my $resp = $client->receive_response;
[download]

https://grep.metacpan.org/search?q=start&qd=Device-Modbus&qft=

https://metacpan.org/release/JFRAIRE/Device-Modbus-RTU-0.022/source/examples/simple_client_rtu.pl