Prof. Fayez F. M. El-Sousy Prof. Fayez F. M. El Prof. Fayez F. M. El - - Sousy Sousy Department of Electrical Engineering Department of Electrical Engineering College of Engineering College of Engineering Salman Salman bin bin Abdulaziz Abdulaziz University University Al Al - - Kharj Kharj , Saudi Arabia , Saudi Arabia Hardware Specifications, Hardware Specifications, Memory Interface and Basic Memory Interface and Basic I/O Interface I/O Interface Microprocessor 8086/8088 Microprocessor 8086/8088
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Prof. Fayez F. M. El-Sousy
Prof. Fayez F. M. ElProf. Fayez F. M. El--SousySousy
Department of Electrical EngineeringDepartment of Electrical Engineering
College of EngineeringCollege of Engineering
SalmanSalman bin bin AbdulazizAbdulaziz UniversityUniversity
AlAl--KharjKharj, Saudi Arabia, Saudi Arabia
Hardware Specifications,Hardware Specifications,
Memory Interface and Basic Memory Interface and Basic
I/O InterfaceI/O Interface
Microprocessor 8086/8088Microprocessor 8086/8088
Prof. Fayez F. M. El-Sousy
Objectives of Objectives of Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� Upon completion of this chapter, you will be able to:Upon completion of this chapter, you will be able to:
�� Describe function of each 8086 & 8088 pin.Describe function of each 8086 & 8088 pin.
�� Understand the microprocessor's DC characteristics and Understand the microprocessor's DC characteristics and
indicate its fanindicate its fan--out to common logic families.out to common logic families.
�� Use the clock generator chip (8284A) to provide the clock Use the clock generator chip (8284A) to provide the clock
for the microprocessor.for the microprocessor.
�� Connect buffers and latches to the buses.Connect buffers and latches to the buses.
�� Interpret the timing diagrams.Interpret the timing diagrams.
�� Describe wait states and connect the circuitry required to Describe wait states and connect the circuitry required to
cause various numbers of waits.cause various numbers of waits.
�� Explain the difference between minimum and maximum Explain the difference between minimum and maximum
mode operation.mode operation.
Prof. Fayez F. M. El-Sousy
�� IntroductionIntroduction
�� In this chapter, the pin functions of both the In this chapter, the pin functions of both the
80868086 and and 80888088 microprocessors are detailed and microprocessors are detailed and
information is provided on the following information is provided on the following
hardware topics: hardware topics: clock generationclock generation, , bus bus
bufferingbuffering, , bus latchingbus latching, , timingtiming, , wait stateswait states, and , and
minimum mode operationminimum mode operation versusversus maximum maximum
mode operationmode operation..
�� These simple microprocessors are explained as These simple microprocessors are explained as
an introduction to the an introduction to the Intel microprocessorIntel microprocessor
family.family.
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
Prof. Fayez F. M. El-Sousy
��Data bus Data bus
�� Internally both are Internally both are 16 bit data bus16 bit data bus
��Externally Externally
��80880888 has has 8 bit8 bit bus AD0 to AD7bus AD0 to AD7
��80880866 has has 16 bit16 bit bus AD0 to AD15bus AD0 to AD15
�� ALE: address latch enable is needed ALE: address latch enable is needed
��Address bus : 20 pinsAddress bus : 20 pins
��Needs a latch to latch the addressNeeds a latch to latch the address
��Most widely used latch is 74LS373 Most widely used latch is 74LS373
��Data bus width is the only major difference.Data bus width is the only major difference.
��Thus 808Thus 80866 transfers transfers 1616--bit databit data more efficientlymore efficiently
��Active high Active high o/po/p signal used after HOLD.signal used after HOLD.
��Indicate that CPU allows to the DMA to Use Indicate that CPU allows to the DMA to Use
buses.buses.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��In Min Mode:In Min Mode:
�� (31) (31) HOLDHOLD –– HoldHold ––
��Active high input from DMA controllerActive high input from DMA controller
��Indicates that device requesting to control the Indicates that device requesting to control the
local buseslocal buses
��SSOSSO –– Status LineStatus Line ––
��For 88 only, an output signal that can be used For 88 only, an output signal that can be used
along with the IO/M and DT/R to decode the along with the IO/M and DT/R to decode the
status of the current bus cycle.status of the current bus cycle.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��In Min Mode:In Min Mode:
��SSOSSO –– Status LineStatus Line ––
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��In Min Mode:In Min Mode:
��For the 808For the 80888/808/80866 in min mode some control signal in min mode some control signal must be generated using logic gate.must be generated using logic gate.
��In max mode these signal are provided by the 8288In max mode these signal are provided by the 8288
��88/86 in min mode provides 3 signals88/86 in min mode provides 3 signals
��RD, WRRD, WR, , andand IO/MIO/M oror M/IOM/IO
��Using these 3 signal 4 important signal must be Using these 3 signal 4 important signal must be generated.generated.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��In Min Mode:In Min Mode:
��These signals are shown in the following table:These signals are shown in the following table:
Never Never
Happened Happened
XX0000
IOWIOW110011
IORIOR111100
MEMWMEMW000011
MEMRMEMR001100
SignalSignalIO/IO/MMWRWRRDRD
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��In Max Mode:In Max Mode:
��Some control signal are generated externally by Some control signal are generated externally by
the the 82888288 bus controllerbus controller
��Some Some pinspins are used for new features available are used for new features available
only for only for Max ModeMax Mode
��Mostly used when Mostly used when CPUCPU is used with Math is used with Math
CoprocessorCoprocessor
��IBM PC/XT and compatible use IBM PC/XT and compatible use 80880888, 808, 80866 with with
80880877 coprocessorcoprocessor
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� In Max Mode:In Max Mode:
�� (24 and 25) (24 and 25) QS0QS0 and and QS1QS1 –– Queue StatusQueue Status ––
�� Give information to the system about the Queue inside Give information to the system about the Queue inside µµµµµµµµp p
at any given timeat any given time
�� In IBM PC these pins are connected to 808In IBM PC these pins are connected to 80877 to synchronize to synchronize
it with 808it with 80888
�� The following table describe their functionThe following table describe their function
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� In Max Mode:In Max Mode:
�� (26, 27 and 28)(26, 27 and 28) SoSo , , S1S1 andand S2S2 Status signalStatus signal
�� Connected to 8288 which will use them to produce all Connected to 8288 which will use them to produce all
control signal such as those shown in tablecontrol signal such as those shown in table
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� In Max Mode:In Max Mode:
�� (29 ) (29 ) LOCKLOCK PinPin
�� Active low Active low o/po/p signalsignal
�� Used to prevent other processor or devices from gaining Used to prevent other processor or devices from gaining
control on the busescontrol on the buses
�� Activated by LOCK prefix in the instruction of the Activated by LOCK prefix in the instruction of the
assembly programassembly program
�� (30 , 31 ) (30 , 31 ) RQRQ / / GT0GT0 and and RQRQ / / GT1GT1 request Grantrequest Grant
�� Bidirectional LinesBidirectional Lines
�� Allow other processors to gain control on the busAllow other processors to gain control on the bus
�� In IBM PC, RQ / GT0 is connected to high making it In IBM PC, RQ / GT0 is connected to high making it
disabled and RQ / GT1 Is connected to 8087disabled and RQ / GT1 Is connected to 8087
��TTLTTL--levellevel peripheral clock signalperipheral clock signal
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
CSYNCCSYNC ((cclock lock
syncsynchronization)hronization)
�� This This activeactive--highhigh signal signal
�� It is used to allow several It is used to allow several
8284 chips to be connected 8284 chips to be connected
together and synchronized.together and synchronized.
�� The IBM PC only uses one The IBM PC only uses one
8284; therefore, this pin is 8284; therefore, this pin is
connected to connected to lowlow..
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
PCLKPCLK ((pperipheral eripheral clclocockk))
�� This frequency is oneThis frequency is one--half half
of of CLKCLK (or o(or onene--sixthsixth of the of the
crystal) with a duty cycle of crystal) with a duty cycle of
50% and is TTL 50% and is TTL
compatible.compatible.
�� In the IBM PC this In the IBM PC this
2.386383 MHz2.386383 MHz is provided is provided
to the to the 82538253 timer to be used timer to be used
to generate speaker tones, to generate speaker tones,
and other functionsand other functions.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
RDY1RDY1 and and AEN1AEN1
�� RDY1RDY1 is active high and is active high and AEN1AEN1
(address enable) is active low. (address enable) is active low.
�� They are used together to provide a They are used together to provide a
ready signal to the microprocessor, ready signal to the microprocessor,
�� which will insert a which will insert a WAITWAIT state to the state to the
CPU read/write cycle. CPU read/write cycle.
�� In the IBM PC, RDY1 is connected In the IBM PC, RDY1 is connected
to to DMAWAITDMAWAIT and and AEN1AEN1 is is
connected to connected to RDY/WAITRDY/WAIT. .
�� They allow the wait state to be They allow the wait state to be
inserted either by the CPU or by inserted either by the CPU or by
DMA.DMA.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
READYREADY
�� This signal is connected to This signal is connected to
READYREADY of the CPU. of the CPU.
�� In the IBM PC it is used to In the IBM PC it is used to
signal the signal the 80888088 to indicate to indicate
if the CPU needs to insert if the CPU needs to insert
a wait state due to the a wait state due to the
slowness of the devices slowness of the devices
that the CPU is trying to that the CPU is trying to
contact.contact.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
RDY2RDY2 and and AEN2AEN2
�� These function exactly like These function exactly like RDY1RDY1 and and AEN1AEN1. .
�� These extra These extra RDYRDY and and AENAEN signals are signals are provided to allow for a provided to allow for a multiprocessing system. multiprocessing system.
�� It allows other generalIt allows other general--purpose CPUs purpose CPUs such as the such as the 8088/80868088/8086 to gain control to gain control over the buses. over the buses.
�� In the IBM PC, In the IBM PC, RDY2RDY2 is connected to is connected to lowlow, , AEN2AEN2 is connected to is connected to highhigh, which , which permanently disables this function permanently disables this function since there is only one since there is only one 8088/80868088/8086microprocessor in the system. microprocessor in the system.
�� In cases of multiprocessor systems, In cases of multiprocessor systems, these signals are used to coordinate these signals are used to coordinate access over the buses by different access over the buses by different CPUs CPUs
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
CLK (clock)CLK (clock)
�� This is an output clock frequency This is an output clock frequency equal to equal to oneone--third third of the of the crystal crystal oscillatoroscillator, or , or EFIEFI input frequency, input frequency,
�� with a duty cycle of with a duty cycle of 33%.33%. This is This is connected to the clock input of the connected to the clock input of the 8088/868088/86 and all other devices that and all other devices that must be synchronized with the CPU. must be synchronized with the CPU.
�� In the IBM PC it is connected to pin In the IBM PC it is connected to pin 1919 of the of the 80888088 microprocessor and microprocessor and other circuitry under the CLK88 other circuitry under the CLK88 label.label.
�� This frequency, This frequency, 4.772776 MHz4.772776 MHz((14.31818 divided by 314.31818 divided by 3), is the ), is the processor frequency on which all of processor frequency on which all of the timing calculations of the the timing calculations of the memory and I/Omemory and I/O cycle are based.cycle are based.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
RESETRESET
�� This is an activeThis is an active--high signal high signal
that provides a that provides a RESETRESET signal signal
to the to the 8088/868088/86 microprocessor. microprocessor.
�� It is activated by the It is activated by the RESRES
input signal discussed earlier.input signal discussed earlier.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
RES (reset in)RES (reset in)
�� This is an input activeThis is an input active--low signal to low signal to
generate generate RESETRESET. .
�� In the IBM PC, it is connected to the In the IBM PC, it is connected to the
powerpower--good signal from the power good signal from the power
supply. supply.
�� When the power switch in the IBM PC is When the power switch in the IBM PC is
turned on, assuming that the power turned on, assuming that the power
supply is good,supply is good,
�� a low signal is provided to this pin a low signal is provided to this pin
�� and the and the 82848284 in turn will activate the in turn will activate the
RESETRESET pin,pin,
�� forcing the forcing the 8088/868088/86 to reset; then the to reset; then the
microprocessor takes over. This is called microprocessor takes over. This is called
a cold boota cold boot.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
OSC (oscillator)OSC (oscillator)
�� This provides a clock This provides a clock
frequency equal to the crystal frequency equal to the crystal
oscillator and it is TTL oscillator and it is TTL
compatible. compatible.
�� Since the IBM crystal Since the IBM crystal
oscillator is oscillator is 14.31818 MHz14.31818 MHz, ,
OSCOSC will provide this will provide this
frequency to the expansion frequency to the expansion
slot of the IBM PC.slot of the IBM PC.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
�� This pin provides an option This pin provides an option for the way the clock is for the way the clock is generated. generated.
�� If connected to low, the clock If connected to low, the clock is generated by the is generated by the 82848284 with with the help of a crystal oscillator. the help of a crystal oscillator.
�� If it is connected to high, it If it is connected to high, it expects to receive clocks at the expects to receive clocks at the EFIEFI pin. pin.
�� Since the IBM PC uses a Since the IBM PC uses a crystal, this pin is connected to crystal, this pin is connected to low. low.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
EFI (EFI (external frequency inexternal frequency in))
�� External frequency is External frequency is
connected to this pin if connected to this pin if F/CF/C
has been connected to high. has been connected to high.
�� In the IBM PC this is not In the IBM PC this is not
connected since a crystal is connected since a crystal is
used instead of an external used instead of an external
frequency generator. frequency generator.
�� In some cases (such as the In some cases (such as the
Turbo PC), this pin is used to Turbo PC), this pin is used to
provide clock frequency in provide clock frequency in
place of place of XIXI and and X2X2..
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
ASYNCASYNC
�� This is called ready This is called ready
synchronization select. synchronization select.
�� An active low is used for An active low is used for
devices that are not able to devices that are not able to
adhere to the very strict adhere to the very strict RDYRDY
setup time requirement. setup time requirement.
�� In the IBM PC this is In the IBM PC this is
connected to low, making the connected to low, making the
timing design of the system timing design of the system
easier with slower logic gates.easier with slower logic gates.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
��The pinThe pin--out of the out of the 8284A8284A clock generatorclock generator
X1 and X2 (crystal in)X1 and X2 (crystal in)
�� XIXI and and X2X2 are the pins to which are the pins to which a crystal is attached.a crystal is attached.
�� The crystal frequency must be The crystal frequency must be 3 times the desired frequency 3 times the desired frequency
for the microprocessor. for the microprocessor.
�� The maximum crystal for the The maximum crystal for the 8284A is 24 MHz and 30 MHz 8284A is 24 MHz and 30 MHz for the 8284Afor the 8284A--1. 1.
�� The IBM PC is connected to a The IBM PC is connected to a crystal of 14.31818 MHz. For crystal of 14.31818 MHz. For some turbo compatibles, it is 24 some turbo compatibles, it is 24 MHz.MHz.
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� The internal block diagram of the The internal block diagram of the 8284A8284A clock generatorclock generator
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� Operation of the Clock SectionOperation of the Clock Section of the of the 8284A8284A clock clock
generatorgenerator
�� Crystal oscillator has two inputs: XCrystal oscillator has two inputs: X11 and Xand X22..
�� if a crystal is attached to Xif a crystal is attached to X11 and Xand X
22, the oscillator , the oscillator
generates a squaregenerates a square--wave signal at the same wave signal at the same
frequency as the crystalfrequency as the crystal
�� The squareThe square--wave is fed to an AND gate & an inverting wave is fed to an AND gate & an inverting
buffer to provide an buffer to provide an OSCOSC output.output.
�� The The OSCOSC signal is sometimes used as an signal is sometimes used as an EFIEFI input to other input to other
8284A8284A circuits in a system.circuits in a system.
�� The following Figure shows how an The following Figure shows how an 8284A8284A is connected to is connected to
the the 8086/80888086/8088. .
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� The clock generator (The clock generator (8284A8284A) and the 8086 and 8088 microprocessors illustrating the ) and the 8086 and 8088 microprocessors illustrating the
connection for the clock and reset signals. A 15 MHz crystal proconnection for the clock and reset signals. A 15 MHz crystal provides the 5 MHz clock vides the 5 MHz clock
for the microprocessorfor the microprocessor
Prof. Fayez F. M. El-Sousy
Hardware SpecificationsHardware Specifications
Microprocessor 8086/8088Microprocessor 8086/8088
�� Operation of the Operation of the ResetReset SectionSection of the of the 8284A8284A clock clock
generatorgenerator
�� The reset section of The reset section of 8284A8284A consists of a consists of a Schmitt trigger Schmitt trigger
bufferbuffer and a and a DD--type fliptype flip--flopflop..
�� thus, this circuit meets 808thus, this circuit meets 80866/808/80888 timing timing
requirementsrequirements
Prof. Fayez F. M. El-Sousy
Memory InterfaceMemory Interface
Microprocessor 8086/8088Microprocessor 8086/8088
�� Two basic types:Two basic types:
�� ROM: ReadROM: Read--only memoryonly memory
�� RAM: ReadRAM: Read--Write memoryWrite memory
�� Four commonly used memories:Four commonly used memories:
�� ROMROM
�� Flash (EEPROM)Flash (EEPROM)
�� Static RAM (SRAM)Static RAM (SRAM)
�� Dynamic RAM (DRAM)Dynamic RAM (DRAM)
Prof. Fayez F. M. El-Sousy
Memory InterfaceMemory Interface
Microprocessor 8086/8088Microprocessor 8086/8088
��The data pins are typically biThe data pins are typically bi--directional in readdirectional in read--write memories. write memories.
�� The number of data pins is related to the size The number of data pins is related to the size of the memory location. For example, an 8of the memory location. For example, an 8--bit bit wide (bytewide (byte--wide) memory device has 8 data wide) memory device has 8 data pins. pins.
��Each memory device has at least one chip select Each memory device has at least one chip select (CS) or chip enable (CE) or select (S) pin that (CS) or chip enable (CE) or select (S) pin that enables the memory device. enables the memory device.
�� This enables read and/or write operations. This enables read and/or write operations.
�� If more than one are present, then all must be If more than one are present, then all must be 0 in order to perform a read or write. 0 in order to perform a read or write.
Prof. Fayez F. M. El-Sousy
Memory InterfaceMemory Interface
Microprocessor 8086/8088Microprocessor 8086/8088
��SRAMsSRAMs
�� SRAMsSRAMs used for caches have access times as used for caches have access times as low as 10ns.low as 10ns.
��DRAMsDRAMs
�� SRAMsSRAMs are limited in size (up to about are limited in size (up to about 128Kb). 128Kb).
�� DRAMsDRAMs are available in much larger sizes, are available in much larger sizes, e.g., 64M X 1. e.g., 64M X 1.
�� DRAMsDRAMs MUST be refreshed every 2 to 4 ms.MUST be refreshed every 2 to 4 ms.
�� Since they store their value on an integrated Since they store their value on an integrated capacitor that loses charge over time. capacitor that loses charge over time.
A circuit that uses eight 2764 A circuit that uses eight 2764 EPROMsEPROMs for a 64K for a 64K ×××××××× 8 section of memory in an 8088 8 section of memory in an 8088
microprocessormicroprocessor--based system. The addresses selected in this circuit are F0000Hbased system. The addresses selected in this circuit are F0000H––FFFFFH.FFFFFH.
A circuit that uses eight 2764 A circuit that uses eight 2764 EPROMsEPROMs for a 64K for a 64K ×××××××× 8 section of memory in an 8088 8 section of memory in an 8088
microprocessormicroprocessor--based system. The addresses selected in this circuit are F0000Hbased system. The addresses selected in this circuit are F0000H––FFFFFH.FFFFFH.
��The The 82C5582C55 is a popular interfacing component, that is a popular interfacing component, that can interface any TTLcan interface any TTL--compatible compatible I/OI/O device to the device to the microprocessor. microprocessor.
�� It is used to interface to the keyboard and a parallel It is used to interface to the keyboard and a parallel printer port in PCs (usually as part of an integrated printer port in PCs (usually as part of an integrated chipset). chipset).
��Requires insertion of wait states if used with a Requires insertion of wait states if used with a microprocessor using higher that an microprocessor using higher that an 8 MHz8 MHz clock. clock.
�� PPI has PPI has 24 pins24 pins for for I/OI/O that are programmable in that are programmable in groups of 12 pins and has three distinct modes of groups of 12 pins and has three distinct modes of operation. operation.
�� In the In the PCPC, an , an 82C5582C55 or its equivalent is decoded at or its equivalent is decoded at I/O I/O ports 60Hports 60H--63H.63H.
��The The 82558255 Programmable Peripheral Interface (Programmable Peripheral Interface (PPIPPI) ) is a 40is a 40--pin DIP IC that provides 3 programmable pin DIP IC that provides 3 programmable I/OI/O ports, ports, A, B, and CA, B, and C..
��How are is it programmable?How are is it programmable?
�� Configure each port as input or outputConfigure each port as input or output
�� Different modes of operationDifferent modes of operation
��You must initialize the You must initialize the PPIPPI via software commandsvia software commands
�� Send a control byte to the deviceSend a control byte to the device’’s control s control