CS321

This Repo contains Assignment Submissions for Peripherals Lab-CS321 by Group 16

• Abhinav Hinger 160101004
• Akhil Chandra 160101011
• Ansh Sood 160101012
• Shimona Verma 160101065

8085 Programming Model

8085 processor has 7 8-bit registers including accumulator and 6 others namely B,C,D,E,H and L.Depending upon requirements,these registers other than Accumulator(A) can be used as Independent Byte Registers or as Register Pairs.

All Addresses and Data Values are to be written in Hexadecimal system.(Eg. LDA 8200H is a instruction and loads the value from Memory location 8200H in the Main Memory to the Accumulator.

Guidelines to Run

1. Download the starter zip from CSE Repo > Hardware and VLSI Lab > HW Lab > esa-xt85.zip
2. Using Adminstrator access , install c16.exe.We will use this to convert our .asm file to .lst and .hex.For additional steps, follow the Help guide from the attached repo.

$ c16 -h test.hex -l test.lst <filename>.asm
$ xt85.exe

3. To run the .HEX file on the microprocessor , start the CMD prompt in Admin mode and run xt85.exe.
4. Before Downloading the file on the board , turn the 1st DIP switch ON (By default) and 4th DIP switch ON to enable the download mode of the 8085 processor.Press RESET to execute the changes.
5. Press Ctrl+D twice to get a Pop-up to enter the File name.Press Enter until the file is completely downloaded.
6. Turn the Download DIP off and press RESET .
7. The file is now downloaded to the board . Follow the steps from the Help Guide to run the program.

Assignments

1. 8-bit and 16-bit Calculator

This program takes 2 Hexadecimal numbers(8bit or 16bit) and another integer to specify the instruction(+,-,*,/). It then calculates the result and stores it in consecutive memory addresses.

1. Addition(A+B):

• For 8-bit ,ADD B instruction is used.It adds the contents of B to the Accumulator A and stores the result in A itself.It also sets the Carry Flag 1 if there is carry which is displayed in next address.
• For 16-bit we used register pair H,L analogous to Accumulator and DAD (Adds Register pair to H,L pair) and sets Carry Flag if carry.

2. Subtraction(A-B):

• For 8-bit ,SUB instruction is used.It subtracts the contents of register specified from the Accumulator A and stores the result in A itself.It also sets the Borrow Flag 1 if there is a borrow.
• For 16-bit ,since the operation is only performed on 8 bits , we subtracted LSB and MSB of the numbers separately First LSBs are operated , the borrow generated from this operation is subtracted from MSB of A.MSB of B is then subtracted from the result.The Borrow bit from this operation is stored in consecutive Memory locations.
• For 8 bit and 16 bit Subtractor,if the result is negative then the 2's complement of the result is displayed by the processor. We converted it back along with the borrow bit(Indicates negative result). Eg 123H - 1234H --> 0001H 1111H (Answer is -1111)

3. Multiplication(A*B):

• We are doing repetitive addition of A , B times.Carry is incremented at every addition if it set carry flag 1.
• As the multiplcation of two 8 bit numbers can be maximum of 16 bits so we need register pair to store the result.
• Same Algorithm is followed for 16 bit numbers.Similar operations for Register Pairs are used (INX,DCX,ORA etc.)

4. Division (A/B):

• We are doing repeated subtraction of B from until A is less than B.The further subtraction will lead to a borrow bit the loop breaks.The number of subtractions done until just before A was negative is the quotient.The closest positive value of A is the Remainder(Calculated by adding B to 1st negative value of A).

2. A) 24 Hour Clock:

• Here we use the T-States of various intructions and Looping them fixed number of times to generate exact delay of 1 Second.Frequency of Crystal Oscillator of 8085 Microprocessor in 2 MHz.Using this we calculated the time a code block takes and generated 1 Second Delay.

• We used various Monitor Routines accessible to user:

  1. UPDAD -Updates Address field of the display
  2. UPDDT -Updates Data field of the display
  3. CURDT -Specific Memory Location
  4. OUTPUT -Outputs characters to display
  5. RDKBD -Reads keyboard. This routine waits until a character is entered from the system keyboard
  6. GTHEX -Gets hex digits and displays them.

• Initially User inputs the starting time after "CLOC" is displayed and presses NEXT to start the clock

• The Second field is updated every second , Minute updated in 60 Second etc. Hour is reset once ir reaches 24 hours

B) TIMER with Interrupt

• Similar code used to generate delay of 1 Second with the Clock running backwards from the Input entered by user
• Minimum Time that can be Measured(Counted Down) by Timer is 1 Min
• We used RST 7.5 (Hardware Interrupt) using KBINT to stop the Timer . See Example 7 of Chapter 8 of the MP5 Manual for more insight.Once stopped,it waits for another key to restart the timer.

3. A) Start/Pause/Halt LEDs

• First we configured the Ports of the 8255 using Control Word (Setting it to 8B) to set Mode = 0 and configure A,B,C ports accordingly.
• Then we compared to input to specific numbers(By ANDing them first and Comparing with the same number) Eg. D5 has to used for Pausing.So D5 bit 1 and rest 0 will make input as 40H.So we do AND and CPI with 40H.If they are equal then we have to pause.
• We paused by looping over the same instructions and checking the input in each iterations(POLLING).We Halted by using RST 5 Interrupt.

B) Elevator Simulation:

• Since Real Lives are at stake We have implemented the Actual Elevator Algorithm.To avoid starvation at any one particular side , the elevator when going in one particular services all requests in that direction and then proceeds to return.
• Due to limited number of LCI board, the lift only brings the people to ground floor from various floors.
• The Boss sits on a fixed floor stored previously (8200H).Any request from BOSS is given top priority and lift proceeds to go towards BOSS to service him at the earliest. Lift takes him/her to Ground floor and then services remaining.
• A register stores the Current floor and B Register stores the Direction in which elevator at any given floor.If there is a request in the same direction as B then lift goes there else it goes in opposite direction.Delay is called to ensure lift travels at normal speed (using same concept as 24HR clock)