4 Pin Diagram of 8085
Fig: pin diagram of 8085
8085 up is an 8-bit general purpose microprocessor capable of addressing 64Kb of memory.
The device has 40 pins,+5 V power supply, operate on 3 to 5 MHZ frequency single phase clock.
All the signals can be classified in 8085 up pin diagram into six groups –
1) Address Bus: in this 16 signals lines. These lines are splits into two segments -
a) A15-A8 – unidirectional and used for the higher order address (MSB).
b)AD7-AD0 – Dual purpose such as data bus as well as lower address data bus(LSB).
2) Control and status signals: these signals are used to identify the nature of operation.
Three control signals that are-
RD – it is a active low signal. Which indicate that the selected IO or Memory device is to be read and data is available on the data bus.
WR-it is a active low signal which indicate that the data on the data bus are to be written into a selected memory or IO location.
ALE- it is a +ve going pulse generated everytime the 8085 begins an operation (machine cycle): which indicate that the bits on AD7-AD0 are address bits.
Three status signals that are –
IO/M- this is a status signal used to differentiate between IO and Memory operations.when it is hign then IO operation and When it is low then Memory operation.
S1 and S0- status signals,similar to IO/M,can identify various operations.that are rarely used in the systems.