What is the correct function or cast to compare an unprintable ASCII character value to a string slice

[Gary Miller]

If I need to examine a byte in string for a specific ASCII value 
like

string MyString;

MyString = "Hello World"

and I want to check a position in the string for a certain 
unprintable ASCII value like the ASCII Block 219 what is the 
recommended method for doing so

if (MyString[0..1])== ???(219)) writeln("ASCII Block found")

I know there's and easy lib function or cast somewhere but 
everywhere I've looked it's not jumping out at me.