Because the documentation is so vast on this, I thought I write a few lines about it.
When specifying a static ack it has a space for both positive and negative values. Unlike all of the other places in the accelerator where you will put either the decimal value or the hex value, in these fields you actually need to past the actual character. A recent client required that a ack be sent back (06 0x06) and that a nak be sent in error (21 0x15). We tried everything until we actually copied from ultraedit into the fields the actual character.
It shows up as a box in the Configuration Explorer, but it sends the SB CR and EB around the character that you have defined in those fields.