EE 308

Solutions to Exam 1

  1. 0xCD = 0b11001101
    0xCD = 205 (unsigned)
    0xCD = -51 (signed)
    Do the following operations on eight-bit numbers. Indicate the answer, and whether a carry (borrow) and/or overflow was generated:

    		68
    + 57     		C5
    + 7B     		23
    + 4E     		D3
    + A4     		00
    - 6D
    Answer BF 40 71 77 93
    Carry (Borrow) No Yes No Yes Yes
    Overflow Yes No No Yes No

  2. Below are some data in the HC11 memory 
         |  0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
-----|---------------------------------------------------------------
0000 | 14  00  B7  23  B4  18  30  18  8F  FE  22  02  5C  E7  03  26
0010 | 0F  CC  0D  10  8E  01  FF  DE  20  EC  02  BD  00  1E  3C  96
0020 | 00  08  1A  94  10  18  38  39  A2  38  9A  05  F2  20  A5  ED
    Show what will be in the registers (in hex) after each of the instructions. If the instruction does not change a register, you may leave that entry blank.
    Instruction A B D X Y SP Addressing
    Mode

    		00000000000000000000
    lds #0x1ff




    		01FFIMM
    ldx 0x0020


    		0008

    		EXT
    ldd 02,x22022202


    		IND
    jsr 0x011e




    		01FDEXT
    pshx




    		01FBINH
    ldaa *0x002cF2
    		F202


    		DIR
    ldab #0x1a
    		1AF21A


    		IMM
    anda 0x001002
    		021A


    		EXT
    puly



    		000801FDINH
    rts




    		01FFINH

  3. Fill in the missing parts (a) through (l) of the assembly listing below. In parts (j) and (l) put in a label, not a number. All other parts should be filled in with hex numbers. 
                                      1 ;
                                  2         .title  EE 308 Exam 1
   0004                           3 LEN = 0x04
                                  4 
                                  5         .area   DATA (ABS)
                                  6         .org    0x20
   0020     0A (a)                7 val1:   .db     10
   0021     C2 00                 8 val2:   .dw     0xc200
   0023     F0                    9         .db     0b11110000
   0024                          10 table:  .ds     LEN
   0028 (b) F6 (c)               11 count:  .db     -10
                                 12 
                                 13         .area   CODE (ABS)
                                 14         .org    0x0100
   0100     DE 21 (d)            15 start:  ldx     *val2
   0102     CC (e) 33 44         16         ldd     #0x3344
   0105     5C                   17         incb    
   0106     E7 04 (f)            18         stab    LEN,x
   0108 (g) 96 23 (h)            19         ldaa    *(val2+2)
   010A     B7 (i) 00 24         20         staa    table
   010D     7C 00 28             21         inc     count (j)
   0110     3F                   22 last:   swi


ASxxxx Assembler V01.50  (Motorola 6811), page 1.
EE 308 Exam 1
Symbol Table

    LEN                             =  0004 
  1 count                              0028 
  2 last                               0110 (k)
  2 start                              0100
  1 table (l)                          0024
  1 val1                               0020
  1 val2                               0021



(a) 0A     (b) 0028     (c)  F6       (d)   21
(e) CC     (f) E7 04    (g)  0108     (h)   23
(i) B7     (j) count    (k)  0110     (l)   table

  4. An HC11 is being used, among other things, as a temperature controller. It reads the temperature from Port C, and turns on and off the heater with Bit 3 of Port B. A subroutine for the HC11 should do the following:
    1. Read Port C
    2. If the value read from Port C (interpreted as an unsigned number) is greater than 7210, clear bit 3 of Port B. Otherwise, set bit 3 of Port B. Leave all the other bits of Port B unchanged.
    3. Repeat (i.e., go to (a)).
    Draw a flow chart and write the program to accomplish the control function. The temperature control part should be called as a subroutine.

    Here is a flowchart:

    Here is a program to implement the flowchart: 

    PORTB      = 0x1004
PORTC      = 0x1003
PROG       = 0x0100
STACK      = 0x01ff
SET_POINT  = 72
;
                .area   CODE (ABS)
                .org    PROG

                lds     #STACK         ;load stack pointer
loop:           jsr     control_temp   ;execute temp control routine
                bra     loop           ;repeat

control_temp:   psha                   ;save ACC A
                ldaa    PORTC          ;read Port C
                cmpa    #SET_POINT     ;compare to set point
                blo     heat_on        ;too cold; turn heat on
heat_off:       ldaa    PORTB          ;too hot, turn heat off
                anda    #0b11110111    ;clear bit 3 of Port B
                staa    PORTB
                bra     done           ;
heat_on:        ldaa    PORTB          ;turn heat on
                oraa    #0b00001000    ;set bit 3 of Port B
                staa    PORTB
done:           pula                   ;restore ACC A
                rts                    ;all done

Bill Rison, <rison@ee.nmt.edu >