readGlobal method
Reads a global variable as a 2-byte word at globalVarAddress
and returns it.
Implementation
int readGlobal(int globalVarAddress){
//if (which == 0) return Z.stack.pop();
if (globalVarAddress < 0x10 || globalVarAddress > 0xff) {
throw GameException('Global lookup register out of range.');
}
//global 0x00 means pop from stack
return loadw(globalVarsAddress + ((globalVarAddress - 0x10) * 2));
}