DETAILS 8085 MICRO-PROCESSOR PIN DIAGRAM
X1 and X2: are clock input pin.
RESET OUT: indicate that micro-processor RESET. This signal can be used to RESET other devices
SID (sid in diagram. my mistake): SERIAL INPUT DATA is input pin used to accept serial one bit data
SOD: SERIAL OUTPUT DATA pin used to send serial 1 bit data
TRAP: it is an EDGE triggered highest priority non maskable interrupt
RST 7.5,RST 6.5,RST 5.5 : these are markable interrupt and have low priority than TRAP
Priority is in the order 7.5>6.5>5.5
INTR and INTA: INTR is a interrupt request signal after which micro-processor generate INTA or interrupt acknowledge signal
AD0-AD7: address data multiplexer bus
A8-A15: tri-state higher order address line
Tri state means it have 3 terminal one normal input and normal out put and one high impedance state . so we can control the output effectively . if there is high impedance state circuit act as a open circuit
IO/M(m bar) : this is output pin or signal used to indicate used to whether 8085 is working in I/O mode (IO/M( m bar)=1 , memory mode (IO/M( bar)=0.
READY: this is an output to check the status of output device. If it is low , the micro-processor will wait until it is high
RESET IN: this is input signal .when RESET IN is low micro-processor restart and starts executing from location 000H
ALE: address latch enable is output signal it goes high when operation is started by processor
SO, SI: these are the status signals used to indicates type of operations
RD: READ is active low input signal to read data from I/O devices or memory
WR : WRITE is an active low output signals used to write data on memory or I/O device
CLK (out) : it is the clock for users ,use for other digital circuits. It’s frequency is same as processor frequency
HOLD&HLDA: HOLD is on input signal this signal indicates that a peripherals requesting the use of address and data bus. In respond to hold micro-processor
Generates HLDA that is HOLD acknowledgement signal
VCC & VSS : power supplied to the micro-processor VCC positive supply And VSS is a negative supply
READY pin is used to communicate slow peripherals
When ALE is high it indicates that bits on AD0-AD7 pins address pin
Working details of S0 and S1
S0 and S1 indicates type of operations
| IO/M (ACTIVE LOW) | S0 | S1 | DATA BUS STATUS(OUTPUT) |
| 0 | 0 | 0 | Halt(stop) |
| 0 | 0 | 1 | MEMORY WRITE |
| 0 | 1 | 0 | MEMORY READ |
| 1 | 0 | 1 | IO WRITE |
| 1 | 1 | 0 | IO READ |
| 0 | 1 | 1 | OP-CODE FETCH |
| 1 | 1 | 1 | INTERUPT ACKNOWLEDGE |
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