From GridLAB-D Wiki
Integers requiring 8 bits are stored in an int8 built-in data type. An int8 value can represent values between -128 to 127.
An attempt to store a value outside that range is unpredictable.
GLM
To declare an int8 value in a class use the syntax
class my_class { int8 my_string; }
To define an integer value in an object use the syntax
object my_class { my_integer 123; }
where "value" is a integer within the range of a 8 bit integer.