Why is this giving me a illegal operands errors? - lc3

Question

I'm trying to write a code in lc3 that will output a block letter using different ASCII characters. When I try to compile my code, I get a ton of errors in the first pass stating I have illegal operands and I'm not sure why.
Here's my code, FONT_DATA points to a bunch of .FILL lines representing the different ASCII characters which I haven't included here:
;Creates the offset needed to find the 16 rows corresponding to the x5002 input
.ORIG x3000
LDI R6,LETTER
AND R8,R8,#0
ADD R8,R8,#16
MULTIPLY ADD R8,R8,#0
BRz ENDOFFSET
ADD R6,R6,R6
ADD R8.R8,#-1
BRnzp MULTIPLY
;Starts the code for the counters
ENDOFFSET ADD R2,R6,FONT_DATA
LDR R5,R2,#0
AND R3,R3,#0
ADD R3,R3,#16
ROWCHECK BRz DONE
AND R4,R4,#0
ADD R4,R4,#8
ROW BRz ROWDONE
;starts code for printing the characters
;this code will print anything with value 0
LDR R5,R5,#0
BRn CHARACTER
LDI R0,NEGCHAR
OUT
BRnzp ENDPRINT
;this code will print anything with value 1
CHARACTER LDI R0,CHAR
OUT
BRnzp ENDPRINT
;this will shift the string and decrement the R4 counter
ENDPRINT ADD R5,R2,R2
ADD R4,R4,#-1
BRnzp ROW
;This will start the next row and increment the string value
ROWDONE ADD R2,R2,#1
ADD R3,R3,#-1
BRnzp ROWCHECK
DONE HALT
CHAR .FILL x5000
NEGCHAR .FILL x5001
LETTER .FILL x5002
Here's my error:
error message
Basically I get "illegal operands for AND" on line 11, and "illegal operands on ADD" for lines 11, 13, 16, and 21. In the first pass

Answer 1

Alright
ADD R8,R8,#16
Firstly the lc-3 has only 8 registers. They are named R0-R7. R8 isn't a valid register.
Secondly the #16 is too big of an immediate value for use with the ADD instruction. The range of values supported needs to fit in 5 bits. That means that the minimum is -16 and the maximum is 15 as these are the numbers you can represent as a 5 bit 2's complement number.
That applies to other instructions where you used R8, or an immediate value higher than 15.
Next this instruction ADD R2,R6,FONT_DATA
Add only accepts a hardcoded number in the immediate value version of the instruction. I suppose you are trying to add the contents of the label pointed to by FONT_DATA and add it to R6. You will need to use the LD instruction to load the value at that address into a register then you can use the ADD instruction with 2 registers.