De-Multiplexing the Address and Data bus 8085 8085 Microprocessor by Ravinder Nath Rajotiya - February 22, 2022February 23, 20220 Introduction 8085 is an 8-bit microprocessor an address a maximum of 216 = 65536 memory location. It has a total of 16-pin on the package which will be used to carry both the address as well as the data. The low order address lines are multiplexed with 8-data lines and hence the pin 11 to 19 on the 8085 microprocessor IC are numbered as AD7 - AD0 (pin 12-19), whereas the high order bus is marked as A15 - A8 (pin 21-28) as shown in following cut-section diagram. For accessing the memory full 16-bit address value must appear at once on pins A15 – A0 but the lower byte is not exclusively available to carry the address, it also carries the data. It
Stack and Subroutines in 8085 8085 Microprocessor by Ravinder Nath Rajotiya - October 13, 2021October 13, 20210 Stack and Subroutines Stack and subroutine are powerful mechanism in 8085 microprocessor for modularizing the assembly program, Stack A stack is a first in last out memory locations in the r/w memory and is used during the execution of a program. This memory is generally specified by the programmer in the main program. To point in the stack memory every processor has a pointer known as the stack pointer. To use the stack, the stack pointer is fist loaded with the beginning address of the stack memory by using the instruction LXI SP, XXXXh. Where XXXXh denotes a 16-bit memory address. The stack may grow up or down. In 8085 the stack grows downward in the reverse order, that means, that once the
Delay Time using 8085 Programming Loops 8085 Microprocessor by Ravinder Nath Rajotiya - October 13, 2021September 29, 20230 Delay Loops in 8085 Loop is used in 8085 for repeating the execution of a set of instructions. Loops are also used in generating the delays in 8085. The Loop is implemented by using the DCR and some conditional JMP instructions. A simple Loop is shown below MVI A, 00 MVI C, 05 Again: DCR C ADD C JNZ again This program make use of a add instruction inside a loop which executed five times. At the end of the loop addition of five numbers 0 to 5 is obtained which is 15. We can also use loop to generate delay time for some applications. The delay is actually the total ‘T’ states times the clock period. i.e. TL =
8085 Memory Organization 8085 Microprocessor by Ravinder Nath Rajotiya - September 24, 2021September 24, 20210 8085 Memory Organization 8085 has 16 address lines, so it can address up to 64KB of memory. This 64KB may be one single IC or can be made using smaller memory IC. The operations on the memory IC can be a memory read or memory write. We can connect the RD’ or WR’ lines from the microprocessor to the coprresponding RD’ and WR’ pins of the memory IC. Thses signals can also be generated by an external logic Figure above shows the necessary signals in addition to the pins on a typical 64 Byte memory module. These signals are: 6 address lines ( because 2^6 = 64) 8 address lines to carry 8-bit of data Control lines as RD’, WR’ and CS’ (chip select) The memory
Timing Diagram 8085 8085 Microprocessor by Ravinder Nath Rajotiya - September 23, 2021February 23, 20220 Timing Diagram 8085 Microprocessor A timing diagram of a microprocessor depicts graphically the activities that are taking place at different instants of time (T states) inside the microprocessor. As discussed previously, microprocessor fetches an instruction from the memory, decodes it, fetches the operands if required and then executes the instruction. An execution of a instruction may take one to six machine cycles and a machine cycle may contain three or more T states. Before we study the timing diagram, the following terminologies should be clear. Instruction cycle – It is the total time by the microprocessor to fetch, decode, fetch operands and execute the instruction. Machine Cycle – It is time taken by the processor in completing the single task, for example fetching an OPCODE,