ECE 3610 MICROPROCESSING SYSTEMS AN ENCRYPTED ASCII CODE DECODER

Transcription

1 ECE 3610 MICROPROCESSIG SYSTEMS A ECRYPTED ASCII CODE DECODER 1

2 PROBLEM SPECIFICATIO Design a microprocessing system to decode messages which are encrypted. Each byte of the message is an encrypted ASCII code. You may use any part from the following in your design: A basic micro-processor (You may use the HC11 or HSC12 instruction set). Three 512x8 ROM chips. Each ROM chip has one active high chip select (CS). One 256x8 ROM chip, with one active high chip select (CS). Eight 32Kx8 RAM chips. Each RAM chip has one active high chip select (CS). One 64x8 RAM chip, with one active high chip select (CS). Many 4-port PCIAs. Each PCIA has one active high chip select (CS). Keypad with given truth table. An ATD converter with the given specifications. A square wave generator with the given specifications. An encrypted ASCII code data supplier with given specifications. ASCII message display unit with given specifications. 2

3 GIVE: KEYPAD KP1 KP0 FUCTIO 0 0 KEY OT PRESSED (KP) 0 1 START PRESSED 1 0 STOP PRESSED 1 1 O FUCTIO KEYPAD KP1 KP0 START STOP 3

4 GIVE: DATA SUPPLIER A device outputs encrypted data as follows: This device outputs encrypted 8-bit words When decrypted, each 8-bit word is an ASCII code. When the device has data ready, it drives its pins with the 8- bit data, and it pulses DR: high-low-high DR Data Supplier 4

5 ECRYPTED ASCII TRUTH TABLE CHAR ASCII CODE UL SOH 01 A1 STX 02 FE ETX EOT F E ECRYPTED CODEWORD CHAR ASCII CODE A B 42 AB C 43 BA D 44 CA E 45 AC F 46 DE G 47 ED H 48 FC I 49 FB J 4A A3 K 4B A5 ECRYPTED CODEWORD 5

6 TOTAL 255 CODEWORDS CHAR ASCII CODE a b 62 AA c 63 FF d e f 66 g h i 69 3F j 6A 77 k 6B 22 ECRYPTED CODEWORD CHAR ASCII CODE DEL 7F B3 C3 FE B2 ECRYPTED CODEWORD 6

7 GIVE: ASCII DISPLAY UIT A device displays ASCII characters To write data to the device: Drive its data pins with an 8-bit ASCII code of the character to be displayed. Then latch the data by providing a negative edge on the LATCH pin. The device will then display the character represented by the ASCII code. LATCH ASCII DISPLAY UIT 7

8 SOLUTIO STARTS HERE 8

9 + 5V PowerOn/Reset Device MIn IRQn RESETn CBUS ABUS μp DBUS The program will continually poll the key pad to input user commands, either START or STOP. VMA Address Decoder φ2 SyRAM_CS PCIA_CS ROM_CS DR DATA SUPPLIER COTROL PAEL START CP1 STOP CP1 A15-A14 8 A8-A0 A5-A0 A4-A0 A8-A0 CS D7-D0 512x8 ROM A5-A0 D7-D0 CS 64x8 SyRAM RS4-RS0 D7-D0 CS 4-Port PCIA PC6 PA7-PA0 PC7 PC4 PC5 PB7-PB0 D7-D0 D7-D0 D7-D0 8 LATCH When the user requests START, the program will execute the following in a loop: Read an encrypted word (byte of data from the DS) Decrypt the byte to ASCII Write the ASCII word (8bit data) to the ASCII Display Unit When the user selects STOP, the program will stop processing the encrypted messages. ASCII CHARACTER DISPLAY DEVICE 9

10 DESCRIPTIO OF DESIG The program will continually poll the key pad to input user commands, either START or STOP. When the user requests START, the program will execute the following in a loop: Read an encrypted word (byte of data from the DS) Decrypt the byte to ASCII Write the ASCII word (8bit data) to the ASCII Display Unit When the user selects STOP, the program will stop processing the encrypted messages. 10

11 Device A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 VMA φ2 ROM PCIA RAM 1 1 x x x x x y y y y y y y y y x x x x x x x x x y y y y y x x x x x x x x y y y y y y 1 1 ROM_CS = A15 A14 VMA φ2 PCIA_CS = A15 A14n VMA φ2 RAM_CS = A15n A14n VMA φ2 ROM_SA: FE00 ROM_EA: FFFF PCIA_SA: 8000 PCIA_EA: 801F RAM_SA: 0000 RAM_EA: 003F 11

12 PCIA EQUATES/MEMORY MAP PCIA_BASE EQU $8000 CRA EQU $8000 DRA EQU $8001 DIRA EQU $8002 IERA EQU $8003 IFRA EQU $8004 PRA EQU $8005 CRB EQU $8008 DRB EQU $8009 DIRB EQU $800A IERB EQU $800B IFRB EQU $800C PRB EQU $800D CRC EQU $8010 KP EQU $8011 DRC EQU $8011 DIRC EQU $8012 IERC EQU $8013 IFRC EQU $8014 PRC EQU $8015 Memory Address PCIA_BASE 8000 CRA 8001 DRA 8002 DIRA 8003 IERA 8004 IFRA 8005 PRA CRB 8009 DRB 800A DIRB 800B IERB 800C IFRB 800D PRB 800E 800F 8010 CRC 8011 DRC 8012 DIRC 8013 IERC 8014 IFRC 8015 PRC Memory Contents 12

13 ROM_BASE EQU $FE00 RAM_BASE EQU $

14 F FFF F 8020 FDFF FE00 FFFF 64 x 8 RAM OT USED 4-PORT PCIA OT USED 512 x 8 ROM The RAM is used for variables and the stack. A ROM is placed at the top of the memory space, because the vector table is designed to be at the top of the memory space in the architecture of the basic μp we are studying in this course. The 4-Port PCIA is mapped from 8000 to 801F. The 4 th port (Port D) is not used. 14

15 SOLUTIO #1 POLLIG METHOD 15

16 Power On or Hardware Reset Reset Function Cf: Page 218, Book LDS SSTACK Hardware Function Software Function PIAIIT Polling 16

17 PCIAIIT FLOW CHART (PORT A) DR DATA SUPPLIER 8 PC6 PA7-PA0 Enter PCIAIIT BSET CRA, $01 Enable PortA: CRA0 1 CLR IERA eed to disable interrupts on these bits for safety. IERA % CLR DIRA BSET PRA, $FF Establish PA7-PA0 as input to receive the 8-bit data from the Data Supplier: DIRA % We don t care about the polarity on the data lines PA7-PA0, but choose something. PRA $FF BCLR IFRA, $FF We don t care about the flags of these bits of Port A, but clear them anyway: IFRA 0 Configure Port B, ext Page. 17

18 PCIAIIT FLOW CHART (PORT B) From Previous Page. LATCH ASCII CHARACTER DISPLAY DEVICE BSET DIRB, $FF BSET PRB, $FF 8 PC7 PB7-PB0 Enable PortB: CRB0 1 BSET CRB, $01 Establish PB7-PB0 as output to send ASCII characters to the Display: DIRB % We don t care about the polarity on the data lines PB7-PB0, but choose something. PRB $FF CLR IERB ot using interrupts on these pins, but need to disable interrupts on these bits for safety. IERB % BCLR IFRB, $FF We don t care about the flags of these bits of Port B, but clear them anyway: IFRB 0 Configure Port C, ext Page. 18

19 PCIAIIT FLOW CHART (PORT C) COTROL PAEL START STOP CP1 CP1 LATCH ASCII CHARACTER DISPLAY DEVICE Enable PortC: CRC0 1 BSET CRC, $01 Establish PC7 as output to latch the data into the Display Device; Establish PC6 as input to receive the DR signal from the Data Supplier; Establish PC5-PC4 as input to receive the Control Panel code: DIRC % BSET DIRC, % BCLR DIRC, % BCLR PRC, $FF 8 PC4 PC5 PC7 PB7-PB0 From Previous Page. Configure the polarity of PC6 to be negative edge sensitive to receive the DR signal, and don t care about the others. PRC % PC6 PA7-PA0 8 DR DATA SUPPLIER CLR IERC ot using interrupts in this example. eed to disable interrupts on these bits for safety. IERC % BCLR IFRC, $FF eed to clear the flag IFRC-6; may as well clear them all: IFRC 0 RTS 19

20 PCIAIIT BSET CRA, $01 CLR DIRA BSET PRA, $FF CLR IERA BCLR IFRA, $FF BSET CRB, $01 BSET DIRB, $FF BSET PRB, $FF CLR IERB BCLR IFRB, $FF BSET CRC, $01 BSET DIRC, % BCLR DIRC, % BCLR PRC, $FF CLR IERC BCLR IFRC, $FF RTS 20

21 ORG RAM_BASE CMD DS.B 1 Enter Polling Subroutine CMD STOP A KP (i.e., DRC) A A % FILTER OUT UWATED BITS CP1 CP0 FUCTIO 0 0 KEY OT PRESSED 0 1 START PRESSED 1 0 STOP PRESSED 1 1 O FUCTIO ext KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 COTROL PAEL START CP1 STOP CP1 PC4 PC5 A==0 Y CMD A UPDATE CMD CMD== START Y Start CMD== STOP Y Stop 21

22 STOP FLOW CHART Enter Stop Subroutine Return From Stop Subroutine stop rts 22

23 ORG RAM_BASE CMD DS.B 1 Enter Polling Subroutine CMD STOP A KP (i.e., DRC) A A % FILTER OUT UWATED BITS CP1 CP0 FUCTIO 0 0 KEY OT PRESSED 0 1 START PRESSED 1 0 STOP PRESSED 1 1 O FUCTIO ext KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 COTROL PAEL START CP1 STOP CP1 PC4 PC5 A==0 Y CMD A UPDATE CMD CMD== START Y Start CMD== STOP Y 23

24 ORG RAM_BASE CMD DS.B 1 Enter Polling Subroutine CMD STOP A KP (i.e., DRC) A A % FILTER OUT UWATED BITS CP1 CP0 FUCTIO 0 0 KEY OT PRESSED 0 1 START PRESSED 1 0 STOP PRESSED 1 1 O FUCTIO ext KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 COTROL PAEL START CP1 STOP CP1 PC4 PC5 A==0 Y CMD A UPDATE CMD CMD== START Y Start 24

25 CMD STOP ext A KP A A % FILTER OUT UWATED BITS update Enter Polling Subroutine A==0 Y CMD A UPDATE CMD cstart ORG RAM_BASE CMD DS.B 1 CMD 0000 Polling ldaa #STOP staa CMD next ldaa KP CMD= CMD= REC anda PLAY #% cmpa #KP beq cstart update staa CMD cstart KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 DRC EQU $8011 KP EQU $8011 CMD= S Y Y Y Record Playback Stop 25

26 DO POLLIG FLOW CHART Enter CMD STOP P_PTR SBUF_BASE R_PTR SBUF_BASE cstart ldaa CMD cmpa #START A KP A A % bne s1 FILTER OUT UWATED BITS jsr start bra next A=0 Y s1 cmpa #STOP bne next jsr stop next CMD A UPDATE bra CMD next cstart CMD== START Y Start KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 s1 CMD== STOP Y Stop 26

27 SIMPLIFIED Enter CMD STOP P_PTR SBUF_BASE R_PTR SBUF_BASE cstart ldaa CMD cmpa #START A KP A A % bne next FILTER OUT UWATED jsr BITS start bra next A=0 Y CMD A UPDATE CMD next cstart CMD== START Y Start KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 27

28 KEYPAD EQUATES KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 CP1 CP0 FUCTIO 0 0 KEY OT PRESSED 0 1 START PRESSED 1 0 STOP PRESSED 1 1 O FUCTIO 28

29 HOW TO DO THE DECRYPTIO 1. Read the encrypted codeword (8-bit data) from the DS 2. Decrypt the byte to ASCII code 3. Send the ASCII code to the message display unit Read codeword Decrypt Display DR DATA SUPPLIER 8 PC6 PA7-PA0 PC7 PB7-PB0 8 LATCH ASCII CHARACTER DISPLAY DEVICE 29

30 TABLE LOOKUP METHOD STEP #1: CREATE A TABLE I ROM org ROM_BASE TableS dc.b $75, $A1, $FE, TableE dc.b $B2 CHAR ASCII CODE UL ECRYPTED CODEWORD SOH 01 A1 STX 02 FE ETX EOT FE B2 30

31 TABLE LOOKUP METHOD STEP #2: CREATE LOOKUP TABLE FLOW CHART/CODE DR DATA SUPPLIER LATCH ASCII CHARACTER DISPLAY DEVICE 8 8 PC7 PB7-PB0 PC6 PA7-PA0 Return found DRB B PULSE LATCH Y Enter start subroutine ASCII CODE = ACCB = 0 X TableS Y DR IFRC6==1 Y IFRC6 0 A DRA A==(X) B B + 1 X X + 1 X==TableE+1 search org ROM_BASE TableS dc.b $75 ;00 dc.b $A1 ;01 TableE dc.b $B2 ;FE start clrb ldx #TableS brclr IFRC,% ,return bclr IFRC,% ldaa DRA search cmpa 0,X beq found incb inx cpx #TableE+1 bne search bra return found stab DRB bclr DRC,% bset DRC,% return rts 31

32 ALTERATIVE TABLE LOOKUP METHOD FASTER AD LESS CODE METHOD Assume we have a 256x8 ROM starting at $0100. The addresses of this ROM would have the 1 st byte fixed at $01, and the 2 nd byte = Encrypted Codeword: ADDRESS B2 DATA FE 01FE 02 ROM CHAR TRUTH TABLE ASCII CODE UL SOH 01 A1 STX 02 FE ETX EOT FE B2 ECRYPTED CODEWORD For examples: We would put $00 at address $0175, since $75 is the encrypted codeword for ASCII $00. $03 at address $0101, since $01 is the encrypted codeword for ASCII $03. $FE at address $01B2, since $B2 is the encrypted codeword for ASCII $FE. ote that this ROM is 100% populated between $0100 and $01FF. 32

33 ALTERATIVE TABLE LOOKUP METHOD FASTER AD LESS CODE METHOD ADDRESS 0100 DATA B2 FE 01FE 02 ROM DR DATA SUPPLIER 8 brclr IFRC, $40, rtn ldab DRA ldaa #$01 xgdx ldaa 0,X staa DRB bclr DRC, % bset DRC, % bclr IFRC, $40 LATCH ASCII CHARACTER DISPLAY DEVICE 8 PC7 PC6 PB7-PB0 PA7-PA0 CHAR TRUTH TABLE ASCII CODE UL SOH 01 A1 STX 02 FB ETX EOT FE B2 ECRYPTED CODEWORD 33

34 ORG RAM_BASE CMD DS.B 1 ORG RAM_BASE+60 ESTACK DS.B 3 SSTACK DS.B 1 Maximum size of the stack is 4 bytes. This occurs when either the Start or Stop subroutine is called within the Polling subroutine. Therefore the stack occupies space from 003C 003F. CMD 0000 ESTACK 003C SSTACK 003F 34

35 FIRMWARE: ASSEMBLY LAGUAGE IMAGE OF DESIG PCIA_BASE EQU $8000 CRA EQU $8000 DRA EQU $C001 DIRA EQU $8002 IERA EQU $C003 IFRA EQU $8004 PRA EQU $C005 CRB EQU $8008 DRB EQU $C009 DIRB EQU $800A IERB EQU $C00B IFRB EQU $800C PRB EQU $C00D CRC EQU $8010 DRC EQU $C011 DIRC EQU $8012 IERC EQU $C013 IFRC EQU $8014 PRC EQU $C015 ROM_BASE EQU $FE00 RAM_BASE EQU $0000 KP EQU $00 START EQU $10 STOP EQU $20 OFUC EQU $30 ORG RAM_BASE CMD DS.B 1 ORG $FFF8 ISR_Vector FDB Main_SA SWI_Vector FDB Main_SA MI_Vector FDB Main_SA RESET_Vector FDB Main_SA Main_SA ORG ROM_BASE lds #SSTACK jsr PIAIIT Loop jsr Polling bra Loop PCIAIIT BSET CRA, $01 CLR DIRA BSET PRA, $FF CLR IERA BCLR IFRA, $FF BSET CRB, $01 BSET DIRB, $FF BSET PRB, $FF CLR IERB BCLR IFRB, $FF BSET CRC, $01 BSET DIRC, % BCLR DIRC, % BCLR PRC, $FF CLR IERC BCLR IFRC, $FF RTS ORG RAM_BASE+60 ESTACK DS.B 3 SSTACK DS.B 1 35

36 FIRMWARE: ASSEMBLY LAGUAGE IMAGE OF DESIG Polling ldaa #STOP staa CMD next ldaa DRA anda #% cmpa #KP beq cstart update staa CMD cstart ldaa CMD cmpa #START bne s1 jsr start bra next s1 cmpa #STOP bne next jsr stop bra next stop rts start brclr IFRC,% ,return ldaa DRA clrb ldx #TableS bclr IFRC,% search cmpa 0,X beq found incb inx cpx #TableE+1 bne search bra return found stab DRB bclr DRC,% bset DRC,% return rts 36