ISCONTROL chechks if a value is between 0 and 0x1f or between 0x80 and 0x9f. Char signess depends of architecture and compiler, so in some environment the second case is always false (and wrong), Techo() calls ISCONTROL with a char variable, whose type cannot be changed because tpuc() expects a pointer to char, so the solution is to insert a cast in the call to ISCONTROL.master