$my_a = array(100, 0, 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
$bin_data = pack("C*", $my_a);
pack() can't take a single array argument, unfortunately. You need to unpack the array into additional arguments.
You can use the following instead:
$packed = call_user_func_array("pack", array_merge(array("C*"), $my_a));
This will basically merge the packing argument with your data array and the function
call_user_func_array() will call
pack() with all arguments extracted from the given array, as single arguments, like needed.
Or alternatively use the splat operator if you're using PHP 5.6+
$packed = pack('C*', ...$my_a);
From the manual: Arrays and Traversable objects can be unpacked into argument lists when calling functions by using the ... operator. This is also known as the splat operator in other languages, including Ruby.
So the array is unpacked into single arguments, just like it is needed by