The following figure shows the pin diagram of the 8085 microprocessor.
Control and Status SIgnals
(Address Latch Enable)
A positive-going pulse is generated every time the 8085 begins an operation (machine cycle). It indicates that the AD7 – AD0 bits are address bits.
Indicates that the selected I/O or memory device is to be read and data are available on the data bus.
Indicates the data data on the bus are to be written into a selected memory or I/O location.
When it is high, it indicates an I/O operation. When it is low it indicates a memory operation.
Status signals similar to . They are rarely used in small systems.
Power Supply and Clock Frequency Signals
+5V Power Supply.
A crystal (or RC, LC network) is connected at these two pins. It is used to give external input to generate clock internally.
Clock Output: Can be used as the system clock for other devices.
Serial I/O Ports
- 8085 has two signals (Serial Input Data) and (Serial Output Data) for serial transmission.
- In serial transmission, data bits are sent over a single line, one bit at a time
Interrupts and Externally Initiated Signals
Vectored interrupts that transfer the program control to specific memory locations.
Nonmaskable interrupt that has highest priority.
Indicates that a peripheral controller is requesting access the use of the address and data buses.
Signal acknowledges the HOLD request.
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 PC is set to 0 and MPU is RESET.
Indicates that the MPU is being reset. This can be used to reset other devices.