MEMORY-MAPPED I /O. Universiti Teknikal Malaysia Melaka. Input/Output System Design

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1 Universiti Teknikal Malaysia Melaka Faculty of Electronics and Computer Engineering Department of Computer Engineering BENM 2123 MICROPROCESSOR TECHNOLOGY Instead of connecting to auxiliary memory, address $ to $7FFFFF can be used to interface to I/O peripherals. Address decoder must be set up to select the address range Program to read and write must pointing to this addresses For example, address $ is connected to 8-bit input switches while the next address is interfaced to 8-bit LEDs The memory-mapped I/O circuitry will be; To Octal buffer CS* From input peripheral Chapter 5: Address bus AS* 23 Address decoder R/W* UDS* LDS* R/W* 06/07 Masrullizam Mat Ibrahim From CS* Octal latch To output peripheral 1 06/07 Masrullizam Mat Ibrahim 3 MEMORY-MAPPED I /O Input/output peripherals are interfaced with in similar way to memory. The technique is called memory-mapped I/O Address decoders are used to mapped the peripherals to specific memory location Some part of memory location is used to communicate to outside world. For example, the training module you use in laboratory has the memory map as below $FFFFFF $A80000 $A7FFFF $A00000 $9FFFFF $ $87FFFF $ Unused area PI/T Illegal address DUART $7FFFFF $ $47FFFF $ $43FFFF $ Unused area Auxiliary memory RAM $ Firmware $ Memory location Normally used to store program data and other important information Memory-mapped I/O Using a memory location to communicate with outside world Operation in either word or byte Activate using address decoder Address Bus AS Address Decoder CPU Data Bus Latch External output device RAM ROM 06/07 Masrullizam Mat Ibrahim 2 06/07 Masrullizam Mat Ibrahim 4

2 Memory-Mapped I/O Vs I/O-Mapped I/O Memory Mapped I/O I/O Mapped I/O PARALLEL INTERFACE/TIMER (PI/T) Capable to perform parallel I/O communications One of the peripheral devices known as PI/T Consists of three bidirectional parallel ports Advantages 1. Any instruction that can access memory can access I/O device 2. Control bus requires one less signal Disadvantages 1. Memory space divided between memory ICs and I/O device 1. Full memory space available for RAM and ROM 2. Separate I/O space is conceptually simple 1. Only accessible through IN and OUT instruction 2. Extra control bus signal required Port PA, PB and PC Each port has eight parallel lines Direction of lines can be programmed Byte and word operation mode also can be set by programming Can be programmed to interrupt the When any port receives new data When 24-bit count down counter reaches Register model of the Port General Control Register (PGCR) Port Service Request Register (PSRR) Port {A,B,C} Data Direction Register (PxDDR) Port Interrupt Vector Register 06/07 Masrullizam Mat Ibrahim 5 06/07 Masrullizam Mat Ibrahim 7 The assembly program can be written as; MOVE.B $440000, D0 ;read from input switches MOVE.B $440001, D1 ;write to output LEDs Or, MOVEA.L #$440000, A0 ;set base address MOVE.B (A0)+, D0 ;read from input switches MOVE.B D0, (A0) ;write to output LEDs Port {A,B,C) Data Register (PxDR) Port {A,B} Alternate Data Register (PxADR) Port Status Register (PSR) Ports A and B be can be used as I/O ports with various handshaking and buffering capabilities in four different modes; Mode 0 Unidirectional 8 bit Transfer on A and B Mode 1 Unidirectional 16 bit Transfer port A in the MSB and port B in LSB Mode 2 Bidirectional 8 bit Transfer on B and bit I/O on A Mode 3 Bidirectional 16 bit Transfer port A in the MSB and port B in LSB 06/07 Masrullizam Mat Ibrahim 6 06/07 Masrullizam Mat Ibrahim 8

3 Figure below illustrates the interfacing between and Based on the PI/T initialization in lab experiments MOVEA.L #$A00001,A0 ;base address for PI/T MOVE.B #$80,+$C(A0) ;set Port A as bidirectional 8-bit MOVE.B #$FF,+$4(A0) ;set all bit Port A as output MOVE.B #$80,+$E(A0) ;set Port B as bidirectional 8-bit MOVE.B #$FF,+$6(A0) ;set all bit Port B as output Set operating mode for each port Mode Value Operation 0 $00 Unidirectional 8-bit transfer on port A and B 1 $40 Unidirectional 16-bit transfer. Port A is MSB, port B is LSB 2 $80 Bidirectional 8-bit transfer on port B, I/O on port A 3 $C0 Bidirectional 16-bit transfer. Port A is MSB, port B is LSB 06/07 Masrullizam Mat Ibrahim 9 06/07 Masrullizam Mat Ibrahim 11 Based on the PI/T initialization in lab experiments MOVEA.L #$A00001,A0 ;base address for PI/T MOVE.B #$80,+$C(A0) ;set Port A as unidirectional 8-bit MOVE.B #$00,+$4(A0) ;set all bit Port A as input MOVE.B #$80,+$E(A0) ;set Port B as unidirectional 8-bit MOVE.B #$FF,+$6(A0) ;set all bit Port B as output Set direction for each port Bit Operation 0 Line (bit) is input port 1 Line (bit) is output Base address for PI/T can also be written as MOVEA.L #PGCR, A0 ;point to port general control register Address for setting direction in Port A can also be written as MOVEA.L #PADDR, A0 ;point to Port A data direction register MOVE.B #$0,(A0) ;set all bit Port A as output 06/07 Masrullizam Mat Ibrahim 10 06/07 Masrullizam Mat Ibrahim 12

4 Example ADC MOVE.B +$10(A0),D0 *get value from adc to D0 MOVE.B #$90,+$12(A0) *turn heater OFF and motor on Port A and B data registers address Value +$10(A0) +$12(A0) Description Port A data register address ($A00011) Port B data register address ($A00013) A more exotic parallel application involve the use of a digital to analog converter (DAC) Figure in page 359 shows the circuitry of a bit DAC is connected to port B of The generation of square, ramp, triangle and sine waveforms can be done using this circuit With the assembly language, the frequency of the waveforms can be modified based on the application of your design Any data accessed via these ports is the data being read from input or written to output peripherals (depends on port direction setting) 06/07 Masrullizam Mat Ibrahim 13 06/07 Masrullizam Mat Ibrahim 15 Analog To Digital Counter Due to our natural environment is analog quantities such as temperature, pressure and strain These input data must be converted to digital value for microprocessor to process them Analog to digital converter such as 8-bit ADC0801 can be used to do the conversion Dual Universal Asynchronous Receiver/Transmitter (DUART) microprocessor 06/07 Masrullizam Mat Ibrahim 14 06/07 Masrullizam Mat Ibrahim 16

5 6821 parallel interface adapter (PIA) 06/07 Masrullizam Mat Ibrahim 17

Parallel Interfacing

Chapter 12 Parallel Interfacing Expected Outcomes Identify the internal registers of MC6821 Design the hardware interface for various I/O devices using MC6821 Develop and write codes using MC6821 Parallel