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UNIT 7 - INTRODUCTION TO I/O INTERFACING

UNIT 7 - INTRODUCTION TO I/O INTERFACING. TWO MAJOR TYPES OF I/O INTERFACING • ISOLATED I/O - DEDICATED I/O INSTRUCTIONS ARE USED TO ACCESS I/O DEVICES (TYPICALLY “IN” AND “OUT” INSTRUCTIONS) - SEPARATE CONTROL SIGNALS FOR MEMORY AND I/O, TYPICALLY: - MEMR IOR - MEMW IOW.

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UNIT 7 - INTRODUCTION TO I/O INTERFACING

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  1. UNIT 7 - INTRODUCTION TO I/O INTERFACING

  2. TWO MAJOR TYPES OF I/O INTERFACING • ISOLATED I/O - DEDICATED I/O INSTRUCTIONS ARE USED TO ACCESS I/O DEVICES (TYPICALLY “IN” AND “OUT” INSTRUCTIONS) - SEPARATE CONTROL SIGNALS FOR MEMORY AND I/O, TYPICALLY: - MEMR IOR - MEMW IOW

  3. • MEMORY-MAPPED I/O SOME OF THE AVAILABLE MEMORY SPACE IS ASSIGNED TO I/O DEVICES. THE I/O DEVICES ARE THEN ACCESSED USING MEMORY-REFERENCE INSTRUCTIONS. - SAME CONTROL SIGNALS FOR MEMORY AND I/O, SUCH AS: - R/W OR - MEMR - ECLK - MEMW

  4. • A MORE EXTENSIVE INSTRUCTIONS SET CAN BE USED TO ACCESS I/O DEVICES. • MORE ADDRESSING MODES ARE AVAILABLE. • SOME OF MEMORY SPACE MUST BE GIVEN TAKEN AWAY FROM MEMORY TO GIVE TO I/O. • MEMORY MAPPED I/O INSTRUCTIONS GENERALLY TAKE LONGER TO EXECUTE. ADVANTAGES OF MEMORY-MAPPED I/O DISADVANTAGES OF MEMORY I/O

  5. “LINEAR SELECT” I/O ADDRESSING (CAN BE USED TO ADDRESS A NUMBER OF DEVICES EQUAL TO OR LESS THAN THE NUMBER OF ADDRESS LINES) A15A14A13A12A11A10A9A8A7A6A5A4A3A2A1A0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

  6. INTERFACE OF INPUT PORT TO DATA BUS WITH NO HANDSHAKING SIGNALS USED Data Bus Device Typically Switches Latch decoder (373) Latch Ox Addr. Bus CLK OE G IOR OR +5V

  7. INTERFACE OF OUTPUT PORT TO DATA BUS WITH NO HANDSHAKING SIGNALS USED Data Bus Device Typically Lights Latch decoder (374) Latch Ox Addr. Bus CLK CP OE GND IOW NOR

  8. INTERFACE OF OUTPUT PORT TO DATA BUS WITHHANDSHAKING SIGNALS GENERATED BY SOFTWARE Latch Data Bus Printer (374) decoder OE CP stb busy Latch GND Ox Addr. Bus NOR Oy Latch CLK Oz gnd oe NOR cp IOW Latch OR oe IOR +5v G

  9. USING I/O PORTS ON THE MC9S12DP256B MICROCONTROLLER

  10. Port Interface Module – Block Diagram

  11. Register x Descriptions • Data Direction Register (DDRx) • I/O Register (PTx) • Input Register (PTIx) • Reduced Drive Register (RDRx) • Pull Enable Register (PERx) • Polarity Select Register (PPSx) • Port Interrupt Enable Register (PIEPx) • Port Interrupt Flag Register (PIFx) • Port Wired-Or Mode Register (WOMx) x: Register Name, e.g., T, S, M, P, H, J

  12. Data Direction Register xx: T, S, M, P, H, J DDRx7 DDRx6 DDRx5 DDRx4 DDRx3 DDRx2 DDRx1 DDRx0 DDRx[7:0] – Data Direction Port I 1 = Associated Pin is Configured as Output 0 = Associated Pin is Configured as Input

  13. Port x I/O Registerx: T, S, M, P, H, J PTx7 PTx6 PTx5 PTx4 PTx3 PTx2 PTx1 PTx0 PTx[7:0] – Port I I/O Register Read Port If Direction is Input, Read State of Pin If Direction is Output, Read State of Buffer Write Port If Direction is Input, Data is Ignored If Direction is Output, Write Buffer

  14. Port x Input Registerx: T, S, M, P, H, J PTIx7 PTIx6 PTIx5 PTIx4 PTIx3 PTIx2 PTIx1 PTIx0 PTIx[7:0] – Port x Input Register Reads State of Pins of Port x If Port x is output, can detect overloads by reading the actual state of the pin.

  15. Reduced Drive Register Port xDirection is Outputx: T, S, M, P, H, J RDRx7 RDRx6 RDRx5 RDRx4 RDRx3 RDRx2 RDRx1 RDRx0 RDRx[7:0] – Reduced Drive Register Port x 1 = 1/3 Full Output Drive 0 = Full Output Drive

  16. Port x Pull Device Enable RegisterDirection is Inputx: T, S, M, P, H, J PERx7 PERx6 PERx5 PERx4 PERx3 PERx2 PERx1 PERx0 PERx[7:0] – Pull Device Enable Register - Port x 1 = Enable Pull Device if Input 0 = Disable Pull Device if Input

  17. Pull Device – Direction is Input • Pull Up – Resistor to +5 Volts • Pull Down – Resistor to Ground Pull up Pull down +5v input cpu cpu input gnd

  18. Port x Polarity Select RegisterDirection is Inputx: T, S, M, P, H, J PPSx7 PPSx6 PPSx5 PPSx4 PPSx3 PPSx2 PPSx1 PPSx0 PPSx[7:0] – Port x Polarity Select Register 1 = Enable Pull Down Rising Edge Sets Interrupt Flag – Ports P, H, J 0 = Enable Pull UP Falling Edge Sets Interrupt Flag – Ports P, H, J Dual Purpose for Ports P, H, J

  19. Port x Interrupt Enable Registerx: P, H, J (Input) PIEx7 PIEx6 PIEx5 PIEx4 PIEx3 PIEx2 PIEx1 PIEx0 PIEx[7:0] – Port x Interrupt Enable Register 1 = Enable Interrupt = Unmask Interrupt 0 = Disable Interrupt = Mask Interrupt

  20. Port x Interrupt Flag Registerx: P, H, J (Input) PIFx7 PIFx6 PIFx5 PIFx4 PIFx3 PIFx2 PIFx1 PIFx0 PIFx[7:0] – Port x Interrupt Flag Register 1 = Interrupt Pending (Write “1” to Clear Flag) 0 = No Interrupt Pending

  21. Port x Wired-OR Mode Registerx: S, M WOMx7 WOMx6 WOMx5 WOMx4 WOMx3 WOMx2 WOMx1 WOMx0 WOMx[7:0] – Port x Wired-OR Mode Register Output Only 1 = Output is Open Drain 0 = Output is Push-Pull

  22. Example

  23. Sample Application • Use Port H[3:0] to Read Inputs from Four Switches with Pull Ups • Use Port H[7:4] to Send Out Four Bits Read from the Switches to a 374 Latch (which is connected to four LEDs) • Use Port J[0] to Provide a Software-Initiated Clock Pulse to the 374 Latch

  24. Example Components Fig. 5.7 374 Latch OE = 0 Enable Outputs “0”->”1” CP Latch Input

  25. Port H Port Definitions(One Method) #define PTH _P(0x260) // port H data register #define PTIH _P(0x261) // port H input register #define DDRH _P(0x262) // port H direction register #define RDRH _P(0x263) // port H reduced drive register #define PERH _P(0x264) // port H pull device enable #define PPSH _P(0x265) // port H pull polarity select #define PIEH _P(0x266) // port H interrupt enable register #define PIFH _P(0x267) // port H interrupt flag register

  26. Port H Port Definitions(Another Method) /* Port H Port Definitions */ #define PTH *(volatile unsigned char *) 0x260 #define PTIH *(volatile unsigned char *) 0x261 #define DDRH *(volatile unsigned char *) 0x262 #define RDRH *(volatile unsigned char *) 0x263 #define PERH *(volatile unsigned char *) 0x264 #define PPSH *(volatile unsigned char *) 0x265 #define PIEH *(volatile unsigned char *) 0x266 #define PIFH *(volatile unsigned char *) 0x267

  27. Port H Initialization /* Initialize Port H */ DDRH = 0xF0; // 7:4 Out, 3:0 In RDRH = 0x00; // Full Drive on Output PERH = 0x00; // Disable Pull Devices on Input //PERH = 0x0F; // Enable Pull DEvices //PPSH = 0x00; // Pull Ups on Inputs (Not Required) PIEH = 0x00; // Disable Interrupts PIFH = 0xFF; // Clear Interrupt Flag Register /* The switches have pull ups and thus microcontroller is not required to supply */

  28. Port J Port Definitions #define PTJ _P(0x268) // port J data register #define PTIJ _P(0x269) // port J input register #define DDRJ _P(0x26A) // port J direction register #define RDRJ _P(0x26B) // port J reduced drive register #define PERJ _P(0x26C) // port J pull device enable #define PPSJ _P(0x26D) // port J pull polarity select #define PIEJ _P(0x26E) // port J interrupt enable register #define PIFJ _P(0x26F) // port J interrupt flag register

  29. Port J Initialization /* Initialize Port J */ /* Set Data Direction Register – Port J Set Bit 0 of Port J to Output Do not change direction of Bits 1 through 7 Read state of Port J Data Direction Register Bitwise Or State with 0x01 Write Data Direction Register – Port J */ DDRJ = DDRJ | 0x01; // Bit 0 is Out

  30. Port J Initialization /* Read State of Reduced Drive Register – Port J Bitwise AND State with 0xFE Write Reduced Drive Register - Port J*/ RDRJ = RDRJ & 0xFE; // Bit 0 is Full Output /* Read State of Interrupt Enable Register – Port J Bitwise AND Value Read Write Interrupt Enable Register – Port J */ PIEJ = PIEJ & 0xFE; // Disable Bit 0 Interrupt /* Init Bit 0 of Port J to 0 */ PTJ = PTJ & 0xFE;

  31. Application Flow Diagram Read Port H Shift Input Bits Left 4 Places Write Port H Latch Strobe PTJ0 = 1 PTJ0 = 0

  32. Application Code /* Read Inputs, Output, Strobe Output into Latches */ PTH = PTH<<4; // Read input, shift 4 left and Output PTJ = PTJ | 0x01; // Set Strobe = 1 PTJ = PTJ & 0xFE; // Set Strobe = 0

  33. Parallel Printer Port Example

  34. Parallel Printer Interface Busy Printer /Strobe Busy Data[7:0] Yes No Write Data Strobe

  35. Parallel Printer Interface Busy J[1] J[0] 68HC12 H[7:0] Printer Latch /Strobe Data

  36. Printer Waveforms Busy Data /Strobe PC Parallel Printer Port Definition www.fapo.com/ieee1284.htm

  37. /* initialize Port H to Output, Full Drive, Printer Data */ DDRH = 0xFF; // Output Direction RDRH = 0x00; // Full Drive /* Bit 0 Port J - /Strobe Output Bit 1 Port J – Busy Input */ DDRJ = (DDRJ & 0xFC)| 0x01; /* Full Drive for Bit 0 Port J */ RDRJ = RDRJ & 0xFE; /* Enable Pull for Input */ PERJ = PERJ | 0x2; /* Use Pull Up on Input */ PPSJ = PPSJ | 0xFD; /* Strobe Initially High */ PTJ = PTJ | 0x01;

  38. Print a Character on Printer void printc(unsigned char c) { /* Wait while Printer is Busy */ while((PTJ&0x02)!=0); /* Printer not Busy, Output Data */ PTH = c; /* Generate Strobe * PTJ = PTJ & 0xFE; // Bit 0 Low PTJ = PTJ | 0x01; // Bit 0 High }

  39. Example – Parallel Interface of 2 Computers(Send Byte from A to B) Port H Out Port J[0] Out Port J[1] In Port H Input Port J[0] In Port J[1] Out Computer A Computer B

  40. Timing Diagrams Port H J[0] J[1] 2 (Sent by Computer A) Valid Data 2 1 3 (Sent by Computer A) Strobe Data 5 4 (Sent by Computer B) Acknowledge Data 6

  41. Computer Software(Pseudo Code) Computer B Initialize: Port H Direction In Port J[0] In Port J[1] Output Port J[1] = 0; Read a byte: Wait for Strobe from Computer A Read Port H; Begin Acknowledge Pulse Wait for Strobe to End End Acknowledge Pulse Computer A Initialize: Port H Direction Out Port J[0] Out Port J[1] Input Port J[0] = 0; Write a byte: Wait until Compute B is Ready Present Data to Comp. B Begin Strobe Pulse Wait for Acknowledge End Strobe Pulse

  42. Computer A // Initialize Port H and Port J DDRH = 0xFF //Port H is Output Port DDRJ = (DDRJ &0xFC) | 0x1; //xxxxx01, J[1] = input, J[0] is output PTJ = PTJ & 0xFE; //xxxxxxx0, send 0 from J[0] //Write a byte while ((PTJ&0x02)!=0); //Wait until Compute B is Ready PTH = data; //Send data out on Port H, to Computer B PTJ = PTJ | 0x01; //Begin strobe pulse to Computer B while ((PTJ&0x2)==0); //Wait until Comp. B has acknowledged data PTJ = PTJ &0xFE; //End strobe pulse to Computer B

  43. Computer B // Initialize Computer B DDRH = 0x00; // //Port H is Input Port DDRJ = (DDRJ & 0xFC) | 0x02; //xxxxxx10, J[1] = output, J[0] is input PTJ = PTJ & 0xFD; //xxxxxx0x, initialize J[1] to 0 // Read a byte while((PTJ&0x01)==0); //Wait until Computer A has sent data Data = PTH; //Read data from Computer A PTJ = PTJ | 0x02; //Begin Acknowledge pulse, sent to Computer A while((PTJ&0x01)!=0); //Wait for Strobe Pulse from Computer A to end PTJ = PTJ & 0xFD; // End Acknowledge pulse, sent to Computer A

  44. ANOTHER EXAMPLEDigital Lock 5 Switches CPU Port H[7] Unlock Port H[4:0] 5 Switches -> Port H[4:0] Port H switches are marked as: A, B, C, D, E

  45. 5 Momentary Contact Switches 5 Switches -> Port H Port H switches are marked as: A, B, C, D, E Port H [0] =“A”, Port H[1]=“B”, Port H[2]=“C” Port H[3]=“D’, Port H[4]=“E” Switches are normally open – “1” in Input Press Switch - “0” in Input Digital Code is Sequence to Unlock Door B, D, E, C, A Detect Sequence to Unlock Port H[7] -- Unlock

  46. Initialize Interface /* Push Button Codes */ #define A 0x1E // 11110 #define B 0x1D // 11101 #define C 0x1B // 11011 #define D 0x17 // 10111 #define E 0x0F // 01111 /* Port H Symbol Definitions */ #define PTH _P(0x260) // port H data register #define PTIH _P(0x261) // port H input register #define DDRH _P(0x262) // port H direction register #define RDRH _P(0x263) // port H reduced drive register #define PERH _P(0x264) // port H pull device enable #define PPSH _P(0x265) // port H pull polarity select #define PIEH _P(0x266) // port H interrupt enable register #define PIFH _P(0x267) // port H interrupt flag register

  47. int main(void) {unsigned char state=0,insw,flag=0; /* initialize the Port H Interface */ DDRH = 0x80; // Bit 7 is Output, Bits 0-6 are input RDRH = 0x00; // Full Drive PERH = 0x7f; // Enable Pull Device (Not Required) PPSH = 0x00; // Enable Pull Up PTH = 0x00; // Bit 7=0 // forever loop while(flag==0) {while((PTH&0x1F)==0x1F); // wait while not pressed // switch was pressed, go process insw = PTH & 0x1F; // read switches

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