Microprocessor - 8085 pin configuration
The following image shows the pin diagram of the 8085 microprocessor -
The pins of an 8085 microprocessor can be classified into seven groups -
Bus with address
A15-A8, it carries the 8 most significant bits of the memory / IO address.
AD7-AD0 , it carries the least significant 8-bit address and data bus.
Control and status signals
These signals are used to identify the nature of the 'operation. There are 3 control signals and 3 status signals.
Three control signals are RD, WR and ALE.
- RD - This signal indicates that the selected IO or memory device should be read and is ready to accept the data available on the data bus.
- WR - This signal indicates that data on the data bus is to be written to a selected memory or IO location.
- ALE - This is a positive pulse generated when a new operation is initiated by the microprocessor. When the pulse becomes high, it indicates the address. When the pulse decreases, it indicates data.
Three status signals are IO / M, S0 and S1.
IO / M
This signal is used to differentiate between IO and Memory operations, i.e. when high indicates IO operation and when 'it is low, it indicates memory operation.
S1 & S0
These signals are used to identify the type of operation in progress.
There are 2 power signals - VCC & VSS. VCC indicates a + 5v supply and VSS indicates a ground signal.
There are 3 clock signals,namely X1, X2, CLK OUT.
- X1, X2 - A crystal (RC, LC N / W) is connected to these two pins and is used to set the frequency of the internal clock generator. This frequency is
- CLK OUT - This signal is used as a system clock for devices connected to the microprocessor.
Interrupts and externally triggered signals
Interrupts are signals generated by external devices to instruct the microprocessor to perform a task. There are 5 interrupt signals, namely TRAP, RST 7.5, RST 6.5, RST 5.5 and INTR. We will discuss interrupts in detail in the interrupts section.
- INTA - This is an interrupt acknowledgment signal.
- RESET IN - This signal is used to reset the microprocessor by setting the program counter to zero.
- RESET OUT - This signal is used to reset all connected devices when the microprocessor is reset.
- READY - This signal indicates that the device is ready to send or receive data. If READY is low, then the CPU must wait for READY to go high.
- HOLD - This signal indicates that another master requests the use of the address and data buses.
- HLDA (HOLD Acknowledge) - Indicates that the CPU has received HOLD and it will drop the bus on the next clock cycle. HLDA is set to low after the HOLD signal is removed.
Serial I / O Signals
There are 2 serial signals namely SID and SOD and these signals are used for communication series.
- SOD (Serial output data line) - The output SOD is set / reset as specified by the SIM instruction.
- SID (Serial input data line) - Data in this line is loaded into the accumulator each time a RIM instruction is executed.