; ---------------------------------------------------------
; A sample PC-231 program to compute and print the alphabet
; This version prints alternating upper- and lower-case
;
; by Fritz Ruehr # CS 231 # Fall 1998
; ---------------------------------------------------------

        DATA #print     ; address of WRITE
        COPY DR,J0      ; set up for jump

        DATA 'Z'        ; finish of alphabet
        COPY DR,R0      ; put 'Z' in R0 for testing
        DATA 'A'        ; start of alphabet

        SET R6,1        ; put upper/lower offset in R6
        SHIFT R6,-5     ; multiply offset; now x20 = 32

#print
        WRITE DR,AD     ; print current letter in ASCII

        COPY DR,R5      ; copy letter for offset in R5
        ADD R6,R5       ; offset letter in R5 to lower
        WRITE R5,AD     ; write out letter in R5

        COPY R0,R1      ; get fresh 'Z' for stop test
        SUB  DR,R1      ; compare current and last letter
        INC DR,1        ; compute next letter

        JPIF R1,NZ,J0   ; continue if compared different
        HALT

; --- End of alphabet program ---