Presentation on theme: "8051 I/O Interfacing Need for more ports PPI 8255"— Presentation transcript:
1 8051 I/O Interfacing Need for more ports PPI 8255 Key board InterfacingLED Interfacing7 Segment LED Interfacing
2 I/O Interfacing I/O Devices connected through ports 8051 has 4 I/O ports P0 to P3.In case 8051 needs external program and/or data memoryP0 and P2 are used for address bus & P0 is used for data bus.Only 2 ports (P1,P3) remain i.e. only 2 I/O devices can be connected.In case system application needs interrupt, serial I/O, i.e. alternate functions of P3Only 1 port (P1) remain i.e only 1 I/O device can be interfaced.
3 In case of 8031(Rom less version ) Program memory is external i.e. (P0 and P2) are not available for I/O interfacing.If P3 in used for alternate functions thenOnly one port (P1) in available.We need more ports.Intel has designed programmable peripheral Interface (PPI) Intel 8255 for this purpose.Intel 8255 PPI has 24 I/O lines distributed to four ports.Port A – (8 Lines)Port B – (8 Lines)Port C – (Upper) – (4 Lines)Port C- (Lower) – (4 Lines)
4 Each port can be programmed to be input or output. Individual port lines can’t be read or written to- different from 8051 ports.Ports have been put in two groups.Group A - Port A and Port C (Upper)(PA7 – PA0) (PC7 – PC4)Group B - Port B and Port C (Lower)(PB7 – PB0) (PC3 – PC0)
6 D7- D0 – Used for data transfer between µp and 8255 (Bidirectional) RD (Input) - Read control SignalWR (Input) - Write control SignalRESET (Input)- Resets the ports. Ports are configuredan input ports on Reset.CS - Used to select the 8255 chip. Chip is selected based on the address decoding.A1, A0 - Are used to select the specified ports in- A1. A0 are lower 2 bits of as address lines.Issued by µp
7 A1 A0Port APort BPort CControl RegisterNote – There is no separate selection for Port C (Upper) or Port C (Lower) Port C is selected as a whole i.e. both upper and Lower ports are selected when A1, A0 = 10.Control Register is used to program thePorts as input or outputProgram the I/O mode.
8 The I/O ports can be programmed to work in any of the 3 modes Mode 0 - Basic Input –OutputMode 1 - Strobed Input-OutputMode 2 - Strobed Bidirectional BusMode 0 – Basic Input-Output majority of application fall under this mode.- Any port A , B, C(U) or C(L) can be input or output
9 Mode 1- Strobed input-output - Provides means for transferring I/O data to or from a specified port in conjunction with strobes or hand shaking signals.- Port C lines are used for hand shaking signals.- Port A and Port B can be used as input or output.- Port A uses port C (Upper) lines for hand shaking – Group A- Port B uses port C (Lower) lines for hand shaking – Group B
10 Mode 2- Strobed Bidirectional Bus Port A can be used for input as well or output for transmitting as well as receiving the data in conjunction with hand shaking signals on Port C.Hand shaking signals are provided to maintain proper bus flow direction5 bits (PC7-PC3) of port C are used for hand shaking. Mode 2 is available for only Group A.Parallely Group B i.e port B can be used in mode 0 or 1.Configuring 8255- We have already mentioned that ports can be configured using control register (A1 A0 = 11).- The control word format for configuration of 8255 is shown
12 Example-We need to configure with Port A as input, Port B as output, Port C (L) as output, port C (upper) as input using mode=00
13 Note – Mode set flag i. e. D7=1 for all configuration Note – Mode set flag i.e. D7=1 for all configuration. If this bit is one then only mode setting with be done by 8255.Thus D7=1 , D5, D6=00-Mode 0, D4=1 (Port A=Input), D3=1[Port C(Upper)=Input], D2=0, (Mode=0) D1=0 (port B=output), D0=0 [ Port C(lower)=output]So the Configuration byte =D7 D6 D5 D4 D3 D2 D1 D0=98 HBy transferring 98H to control Register of 8255 will configure 8255 in the above manner.How -? We shall see after interfacing of 8255 with 8051.Note – The concept of 8255 configuration using control register has been used in 8051 in case of Timer, Serial I/O and interrupts.1
14 I/O and memory are treated separately 8255 – 8051 InterfacingLet us review I/O mapped I/O and memory mapped I/O [Ref. Page of Krishna Kant book.]In I/O mapped I/O- The µp has separate instructions for memory and I/O read-write.In addition µp will have separate control signals for I/O read-write and memory read-write.A variation of this may be that µp has same read-write control signal for I/O and memory but may have another signal to identify whether the read-write is for memory or for I/O.I/O and memory are treated separatelyExample – 8086 has IN and OUT as I/O read and write instructions. It has same RD (for read),WR (for write), signal for I/O and memory read- write. It has M/IO to identify memory or I/O read-write.
15 In Memory mapped I/OI/O ports are treated as memory locations.µp having memory mapped I/O.Will not have separate instructions for I/O and memory read-write.Will have only single read and write control signals for read and write.Will not have any signal to identify memory or I/O read-write.Example -8051 has no separate instructions for memory and I/O read - write8051 has only single read and write control signal
16 PSEN – external program memory read RD – External data memory readWR - External data memory writeIt has no signal to indentify whether read - write in for I/O or memory.Thus – I/O ports are treated as memory locations.Thus if we have to interface 8255 to 8051 , 8255 must be interfaced in external memoryExternal program memory can’t be written to .Thus 8255 must be interfaced in the external data memory.We need to select the address ‘XXXXH’ of 8255The address on address lines to be decoded such that when ‘XXXXH’ is there, CS for 8255 is generated i.e 8255 needs to be selected.
17 RD (8051) connect to RD (8255)WR (8051) connect to WR (8255)Movx instructions to be used for data transfer from / to 82558255 has four portsWhen address linesA1 – A0 = 00 - Port A is selected= 01 - Port B is selected= 10 - Port C is selected= 11 - Control register is selectedThus last two bits starting address of 8255 address must be 00
18 Assume that 8255 is interfaced at address FE10H Port A address = FE10HPort B address = FE11HPort C address = FE12HControl register address = FE13HMOV DPTR, # FEI3HMOV A, # 98HA(will configure 8255)MOV DPTR, # FE10HMOVX DPTR(will bring the content of Port A to ACC.)
19 To generate CS for 8255 from given address. Assume address = FE10 F EA1 , A0 are directly connected to 8255 and used for selection of I/O ports A,B,C and Control Regester.For selection of 8255 through CS, the address bits A2 to A15 may be decoded using simple gates.1
20 Many Variations of circuits are possible CS of 8255A7A6A5A4A3A2Many Variations of circuits are possible
21 If we select 8255 address as 0030H then decoding may be- A5 A4 A7A6A5A4CSA3A2
22 But it will generate Cs for 8255 for all address where A7 to A2 = 00 11 00 i.e. 0030H, 0130H …………….FF30HAll these address will be valid for 8255 selection and are called address aliases – (aliases is used in general for other names identifying a person)Problem - 1If selected address for 8255 = 8000H i.e.What will be decoding strategy ?
23 Problem -2If 8255 address = 1110HThen what will be decodingDecoder 74LS138 may also be used.
24 A15A12A1 A0CS of8255ORA15A14A13A12A11A10A 9A 8Decoding of 8255 Address E000H to generate chip select
25 Reading and writing to 8255 ports Let us assume that 8255 has been interfaced at address E000H the port addresses will bePort A - E000HPort B - E001HPort C - E002HControl register - E003HConsider that the application demands the following ports configurationPort A - OutputPort B - InputPort C - OutputMode = 0What will be control word of 8255 ?
26 The 8255 control word will be-1000 0010 =82H We may configure 8255 by writing 82H to control register in two ways:-(A)MOV DPTR, # E003HMOV A, # 82HNote - E003 is location in external data memory.Other way of writing (A) will be(B)PRA EQH E000HPRB EQH E001HPRC EQH E002HPRCR EQH E003HORG 00HSJMP 030HORG 030H
27 MOV DPTR, # PRCRMOV A, # 82HATo read data from Port BMOV DPTR, # PRBMOVXTo write data to Port AMOV DPTR,# PRAMOV A,# DataA
28 Note :- 8255 ports ie . A,B,C have no addressable bits. That to find status of individual bits –Read port contextUse logical operations ANL ORL etcOr- Use shift/rotate RRL , RRL etcIn keil bit (24 MHz, 8051) 8255 has been interfaced at addres E000HIn program (B) way of writing is normally used.Now let us take some I/O interfaceWe shall first take upKeyboard interfacing followed byLED interfacing and7 segment LED interfacing
29 Basic keyboard operation is shown in figure Keyboard interfacingBasic keyboard operation is shown in figureINHighOUT (High when the key is pressed)Basic keyboard operation-single key.
30 Basic keyboard operation- two keys. OUT 1OUT 2IN
31 Basic keyboard operation – four keys. OUT 3OUT 2OUT 1OUT 4INBasic keyboard operation – four keys.Above Configuration can’t be adopted for more no. of keysA 64 key keyboard will require 8 bit portsWe may represent the above as.
33 Contains two rows – IN1 and IN2 and two columns OUT1 and OUT2 Activate Row1 i.e IN1 check OUT1 (If 1 then key No. 1)Else cheek OUT2 (If 1 then key No. 2)Activate Row2 i.e IN2 check OUT2 (If 1 then key No. 3)Else check OUT2 (If 1 then key No. 4)8 x 8 key board can be arranged in 8 rows and 8 columns.Only two ports are required to interface with µp.
35 Code table for 8 x 8 keyboard The codes of keys of key board may be staored row wise is memory.When a Key is pressed.row no. and column no.i.e. position of key is identifiedkey code is taken from table and used in the program.XX1Codes for keysin the first rowCodes for Keysin the second rowin the eighth rowXX2XX8Code table for 8 x 8 keyboard
36 Keyboard- microprocessor interface software flowchart StartIEnable the Ith rowSet the address of the code for the first key on this rowCheck for key depressionKeyDepressed?Determine the column number and the code of the keyI I+1I>8YesNo
37 Key DebouncingWhen a key is depressed and released contact is not broken permanently.Key makes and breaks the contact several time for few milliseconds before the contact is broken permanently.Thus a key depression detected by µp may be false i.e it may be due to bouncing of key.Thus key debouncing i.e. as certaining that key depression in true is important.Debouncing by HW and SW both in possible.Software debouncing after key depression detected.µp executes a delay routine for few milliseconds.µp then again checks for key depression.If key is depression is detected then real depression else false depression.
38 Let us interface 4x4 keyboard with 8051 Both rows and columns can be connected to 8 lines of one port.Rows can be activated by using SET B bit instruction.Key Depression can be checked by using JB or JNB instructions.Hex key pad interface in Lab.- 16 keys (0 to F) arranged in- 4 x 4 key boardRows connected to – PB0 to PB3Columns connected to – PA0 to PA3You have to determine the key depressionStore the code of the key in memory.
40 LED Interface LED i.e Light Emitting Diode emits light energy when conductsAnode is held at higher voltage than cathod+5 VLED operation.
41 LED interface with microprocessor Common cathode Anode connected to Port LinesAll cathodes connected togetherto grounds[ Port bit = 1LED Conductsi.e glows ]PortBit 7Bit 0Microprocessor interface to LED (common cathode)
42 Common Anode Anodes of all LED’s connected together to 5V Cathodes of LED’s connected to port lines[ Port bit = 0LED Conductsi.e glows ]Bit 7Bit 0+5 VMicroprocessor interface to LED (common anode).
43 In common cathode- by making individual port bits as “1” we may glow the LED. SETB P2.7 i.e LED connected to P2.7 will glowMOV P2,#OFFH – All LED’s connected to port Port P2 will glowIn common Anode making a particular port bit ‘0’ will glow the LED connected to the port line.CLR P2.7- LED connected to P2.7 will glowMOV P2, # 00H- Will glow all the LED’s connected to port P2.
44 Example :- For displaying A, all segments except d and h should glow. Seven segment LED’s – The LED’s can be arranged in the fashion shown inabcdefghThe structure has eight segments a,b,c,d,e,f,g and h. Very use full in displaying numeric and alphanumeric data.Example :- For displaying A, all segments except d and h should glow.
45 Character formation in seven segment LEDs bcefgd
46 For displaying 6, all segments except b and h should glow. h is used for displaying decimal point.Note – Previously there were only seven segments. Eighth segment h has been added later. But name seven segment has remained stock.The On/Off in formation of segments can be arranged in one byte.Called control byte for 7 segment LEDThe bits (port lines) can be connected to segments as common catnode or common anode fashion.Common Catnode - Anodes connected to bits catnodes connected to ground.Common Anode – Anodes connected to +5V catnodes connected to bit.
47 Representing segment code in byte - two ways a b c d e f g hh g f e d c b a0-Glow the segment for common Anode configuration1-Do not glow
48 Common Catnode - bit =1, segment glows bit = 0 – doesn’t glowCommon Anode - bit = 0 – segment glowsbit = 1 – segment doesn't glowMicroprocessor can be interfaced to seven segment LED in parallel or serial way.
49 … Parallel interface +5 V Anode a b h Resisters Out port 7 6 Microprocessor interface to seven-segment LED (parallel interface).
50 in common Anode fashion Cathode of segments – connected to port bits.MOV Px, #00H – will glow all the segmentsCLR Px .3 – will glow segment No. 3 i.e segment ‘e’.Simple Hard ware and software interfaceFor one 7 segment LED i.e display of 1 character one port is dedicated.Thus for displaying 20 characters, 20 ports will be required. Generation of ports will require extra hardware.Parallel interface is very fast but we don’t require very fast changing display due to limitation of our eyes.Serial Interface- Over comes the limitation of parallel interface in case of large no. of 7 segment displays.
51 … +5V Anode a b c d e f g h a b h Resisters MSB LSB Shift register Code bitsClockMicroprocessor interface to seven-segment LED(serial interface)
52 Contains – shift register connected to 7 segment LED. Two input lines- one for code bits and other for clock.The operation sequence is shown inStartLoad LSB fromdisplay codeLoad clockLoad next bitNoSeventhbit loaded?Load clockYesStop
53 After 8 clock period the character will appear in 7 segment. Example:- Display code for A1h g f e d c b aafbgfor common anode configuration .ec
54 As bits move in shift register different segments glow and at the end of 8 clock periods ‘A’ appears.Connecting more segments doesn’t require any extra port or line. Using just clock and code bit line we may connect many segments in serial fashion. MSB of a segment is connected to input code bit line of shift register of next segment.
56 The characters will appear almost instantenously. Large No. of 7 segment displays can be connected74164 shift register is normally used. Any two port lines-one for clock and other for code bits may be used for displaying.Control byte may also be arranged asa b c d e f g hIn this case we shallInput MSBInput Clock
57 And continue doing it After 32 clocks, the 4 characters will appear in 4 -7 segment LED’s Coder bits of characters to be displayed may be stored in consecutive memory locations.D0 D1 D2 D3Code bits are sent in the order of D0 to D3.A segment counter is initialized to 32.After every clock – decrementedWhen counter =0, - stop i.e. operation is completed7 segment display experiment is port of microcontroller lab.
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