try something like this (taking your 1st serout line as an example):

Serout Tx, N9600, [$44,$00,$A0,$E4]

$A0 is just 160 in hex.

To work out the sum: $44+$00+$A0=$E4

If the sum is bigger than $FF then you take just the lower byte. e.g. if the sum came to $01A2, then you just use $A2.