Could some one explain how this is used when using the DB directive. I'm trying to follow someone elses code who has since left. I'm having real trouble grasping how the following code works:

xch a,r7
add a,#3
movc a,@a+PC
ljmp PLU20&P_SUFFIX
;Memory translator.
DB 28H,28H,28H,28H,28H,28H,28H,28H ;IN1
DB 29H,29H,29H,29H,29H,29H,29H,29H ;IN9
DB 2AH,2AH,2AH,2AH,2AH,2AH,2AH,2AH;IN17
and on and on

Any Help is appreaciated.
Thanks
Brian