Hi Pesti,
What kind of data is stored in ADVAL? What I am going to say may not be right, it is worth investigating on your part however . . . DEC forces HERSEROUT to send data as Decimal numbers. When you send without using it, I think it is going out as ASCII. Apparently your "reciever (I.E. computer, serial LCD . . . )" is expecting ASCII. To communicate both devices must speak the same language.