Pin Diagram of 8085:
The 8085 is 8-bit microprocessor which is produced by INTEL .
it has 40 pin . Now we will discuss about Intel 8085
(i) x1, x2(Pin1,2): Thiese pins are used for connecting an xternl clock circuit, Which can be either be a cristal or a LC network or a RC network. The internal frequency is converted to the half of the crystal frequency.
(ii) Reset out(pin3) : A high appears at this pin when 8085 is reset . The signal indicates that the microprocessor is being reset. The signal can be used to reset other device.
(iii) SOD- SID(pin4,5) : In 8085 , serial transmission is implemented by two signals SOD, SID (serial input /output data) for transmitting serial data respectively.
(iv) TRAP(pin 6): TRAP is having the highest priority interrupt.
(v) RST 5.5 To RST 7.5(pin 7 to 9): The restart interrupt help in transferring program cotrol to spwcific memory location.
(vi) INTR & INTA (pin 10,11) : INTR is the interrupt with having lowest priority.
INTA is used for acknowledging and interrupt request . Wen this pin having low signals , it acknowledgeing the request .
The order of priorities these interrupt TRAP>RST&>%>RST>6.5>RST5.5>INTR
(Vii) AD0 to AD7(PIN 12 to19) : The 8 bidirectional signal lines AD0 - AD7 are used as dual purpose multiplex address 5 pin data bus. These are used for transferring data as well as lower order address bus.During the excution of an instruction these lines are used as lower order address bus is the earlier part of the cycle and the later part of the cycle . Three pins are used as data bus , Hower a LATCH is used to seperate of the address bus from this multiplexed signal.
(Viii) vss(pin20) : its ground reff. it is reffered to be zero volts.
(ix) A8 to A15( pin 21 to 28) : The 8085 has 8 unidirectional signal lines which are used for transmission the high order sddress bus.
(x) S0, S1(pin 29,33) : These status signals similar to I0/m can identifying various operation but they are really used in small system.
(xi) ALE (pin 30) : ALE stands for Address Latch Enable . This is a positive growing pulse generated everytime the 8085 brgins an operation . It indicates that the bits on AD0 - AD7 are address bits . This signal used primarily to LATCH the low order address from the multiplexed bus and generate a seperate set of eight address line (A0-A7).
(xii) WR (Write pin 31) : This is a write control signal (Active low) . This signal indicates that the data on the data bus are to be written into a selected memory on I0 location.
(xiii) RD(Read pin 32) : This is a Read control signal . This signal ndicates that the selected I0 or memory devices is to be read and data are available on the data bus.
(xiv) I0/M(pin 34) : This is status signa used to differentiation between I0 and memory operations. When it is high it indicates an I0 operation. When it is low , it indicates a memory operation.
(xv) READY(pin 35) : This signal is used to delay the microprocessor . READ or WRITE cycles until a slow responding peripheral is ready to send or accept data. When this signal goes low, the microprocessor waits for an integral number of clk cycle until it goes high.
(xvi) RESET IN (Pin 36) : where the signal on this pin goes low the program counter is set to zero and the microprocessor is RESET.
(xv) CLK OUT(pin 37) : This signal can be used as the system clock for other devices.
(xvi) HOLD( pin 38) : This signal indicates that a peripheral such as DMA (Direct Memory Access ) controller is requesting the use of the address and data buses.
(Xvii) HLDA(pin 39) : Output hold Acknowledge , this signal acknowledge the hold request.
(xviii) Vcc(pin 40) : +5 volt power supply.
Shortly if we see the main thing
> Status signal : S0,S1, I0/m
> Control signal : WR, RD
> Interrupt: TRAP to INTA
>Serial Transmission : SOD, SID