Design lab II
1
Design Lab II : Report Elevator Control Mechanism
Prasant Kumar Umang Mahajan Gritika Valechha Shreya Ganguly
001110501044 001110501044 001110501047 0011 10501047 001110501055 0011 10501055 001110501056 0011 10501056
Design lab II
2
INDEX
Problem Statement
3
Equipment Catalogue
4
Design Overview
5
Scheduling Algorithm
6
Interfacing With The Kit
9
Code
10
Further Considerations
15
Acknowledgements
16
Design lab II
3
PROBLEM STATEMENT
The main task of the lab assignment is to design an Elevator Control Mechanism for a single elevator system using the 8085 Microprocessor Training kit (VMC-8506) and other peripherals as required.
Design lab II
4
EQUIPMENT CATALOGUE •
•
•
•
•
•
• •
8085 based microprocessor trainer kit 14 LEDs 6 Push Buttons 26-pin FRC connector Connecting wires +5V D.C. power supply 20 100ohm resistors Bread Board
The kit provides a 8 bit microprocessor (8085-A) interfaced with 8K bytes of RAM using 6264 and 8K bytes of EPROM using 2764 loaded with powerful monitor programs. The monitor is incorporated from 0000h to 1FFFh and the RAM has an address from 2000h to 3FFFh. Additionally the training kit has got a 16 bit programmable timer/counter using 8253 and 24 I/O lines using 8255 PPI. 8 different levels of interrupts are provided using 8259. Besides other features, the kit also provides 6 seven segment display and a 28 key keyboard. The power requirement of the kit is +5V, 1.5A.
Design lab II
5
DESIGN OVERVIEW Initial settings and assumptions: • • • •
There are a total of 4 floors in the building ranging from floor 0 to floor 3. The elevator cabin is initially at floor zero (ground level). There are no requests and the corresponding LEDs are off. The elevator services requests in one direction at a time and then reverses direction to serve the remaining requests in that direction. • If there are no more requests to service then the elevator stays at the last floor serviced until a new request has been made. We use push buttons to request service from the elevator. There are two push buttons allotted for each level(floor) except the topmost and the bottom most floors for obvious reasons. The button(s) indicates the direction in which the user wants to go. When a button is pressed the corresponding LED glows to indicate that a request is made. If the request lies in direction of motion(remaining) of the elevator it is serviced otherwise it is kept in memory and serviced in the next turn as per the scheduling algorithm mentioned later. The current location(floor) of the elevator is displayed in the data segment of the display present in the kit. Its motion(ascent or descent) is shown by two LEDs. Once inside the cabin of the elevator, the user can input its desired destination using the keyboard provided in the kit. No provision has been made to show the destination selected by the user.
Design lab II
6
SCHEDULING ALGORITHM We have stored the ascent and descent in separate memory locations as bit patterns consisting of 4 bits each. The upper nibble in both cases is set to 0000. When a particular request(ascent or descent) is made, then the content of the corresponding memory location is updated by setting the requisite bit according to the floor the request came from(Suppose a request came from floor n for ascent. Then the nth bit in the contents of the memory location for ascent is set to 1). The elevator operates continuously in two cycles, an UP cycle and a DOWN cycle. When servicing the UP cycle, requests are serviced from LSB to MSB of the contents(lower nibble). If any bit is set to 1, then the elevator stops at that floor, resets the corresponding bit to 0 and resumes ascent. In the DOWN cycle, requests are serviced from MSB to LSB of contents(lower nibble). The same logic is followed for updating the corresponding memory location contents. (note: this system is valid for 4 floors). The various cases that may arise during the motion of the elevator has been captured and tabulated in the following table. (see next page to understand the working of the last row). Elevator Ascent User Ascent
Elevator Descent
User Descent
User current level < Elevator current level
User current level > = Elevator current level
User current level < Elevator current level
User current level > = Elevator current level
Request to be processed in the next ascent.
Request to be processed in the current ascent.
Request to be processed in the following downward descent.
Add the request level to the next min heap (min_heap#2 ) and Heapify!
Add the request level to the current min heap (min_heap#1 ) and Heapify!
Add the request level to the current max heap (max_heap#1) and Heapify!
User Ascent User current level < Elevator current level
User current level > = Elevator current level
User Descent User current level < Elevator current level
User current level > = Elevator current level
Request to be processed in the following upward ascent.
Request to be processed in the current descent.
Request to be processed in the next descent.
Add the request level to the next min heap (min_heap#2) and Heapify!
Add the request level to the current max heap (max_heap#1 ) and Heapify!
Add the request level to the next max heap (max_heap#2 ) and Heapify!
Design lab II
7
When the number of floors is large: A more efficient method would be to maintain separate heaps for ascent and descent. The various operations performed according to the nature of the inputs are described in the table in the previous page. This is not necessarily for an 8085 microprocessor based system. It can be generalised for other high level language implementations. The destination levels are selected from the heap#1 (min_heap#1 for elevator ascent phase and max_heap#1 for elevator descent phase). After the completion of a particular phase the heap#1 for that phase is assigned the values of heap#2 and heap#2 is cleared. Since min/max heap is used for ascent/descent , the destination closest to the elevator’s current location in sync with the motion of the elevator is serviced first, thus eliminating the possibility of the elevator performing to and fro motion between specific (highly used) levels. The flowchart for the working of the elevator is shown below :
Design lab II
8
Design lab II
INTERFACING WITH THE KIT We make use of the 8255 Programmable Peripheral Interface provided on the kit to connect the push buttons and LEDs with the processor. We use the 8255 in Mode 0, with Port B as input for the push buttons and Port A and Port C as outputs for the LEDs. The control word fed to the 8255 for setting the above configuration is 10000010. The interfacing circuit is shown below.
9
Design lab II
PORT A EQU 00 PORT B EQU 01 PORT C EQU 02 CWR EQU 03
10
CODE
Design lab II MEMORY LOC
11 ASSEMBLY CODE
MACHINE CODE
3000
MVI C,00
0E 00
3002
MVI A,82
3E 82
3004
OUT 03
D3 03
3006
MVI A,00
3E 00
3008
OUT 00
D3 00
300A
CALL DISPLAY
CD 0025
IN 01
DB 01
300F
MOV B,A
47
3010
ANI 07
36 07
3019
JNZ Y
C2 1F30
301C
MOV A,B
78
301D
ANI E0
EC E0
JZ X
CA 11 30
MVI D,00
16 00
MVI E,01
1E 01
RRC
0F
3024
JC P
DA 37 30
3027
INR D
14
3028
JMP L
C3 23 30
302B
MVI D,03
16 03
302E
MVI E,00
1E 00
RLC
07
3030
JC P
DA 37 30
3033
DCRD
15
3034
JMP L1
C3 2F 30
MOV A,C
79
3038
CMP D
BA
3039
JC UP
DA 53 30
303C
JNZ DOWN
C2 68 30
3041
CMP E
BB
3042
JZ L2
CA 4A 30
300D
301F
LABEL
X
Y
3021 3023
302F
3037
L
L1
P
Design lab II
12
3045
MVI H,43
26 43
3047
JMP L3
C3 4C 20
304A
L2
MVI H,42
26 42
304C
L3
MOV L,C
69
CALL CLEAR
CD 00 40
ASSEMBLY CODE
MACHINE CODE
JMP X
C3 11 30
CALL DELAY
CD 00 41
3056
INR C
0C
3057
CALL DISPLAY
CD 00 25
305A
MVI H,42
26 42
305C
MOV LC
69
305D
CALL CLEAR
CD 00 40
3060
MOV A,C
79
3061
CMP D
BA
3062
JNZ UP
C2 53 30
3065
JMP X
C3 11 30
CALL DELAY
CD 00 41
306C
DCR C
0D
306D
CALL DISPLAY
CD 00 25
3070
MVI H,43
26 43
3072
MOV L,C
69
3073
CALL CLEAR
CD 00 49
3076
MOV A,C
79
3077
CMP D
BA
3078
JNZ DOWN
C2 68 30
307A
JMP X
C3 11 30
MOV A,H
7E
OUT 00
D3 00
304D
MEMORY LOC
LABEL
3050 3053
3068
4000 4001
UP
DOWN
CLEAR
Design lab II
13
4003
MVI A,FF
3E FF
4005
OUT 00
D3 00
4007
RET
C9
PUSH B
C5
4101
PUSH D
D5
4102
PSW
F5
4103
MVI B,0A
06 0A
LXI D,FFFF
11 FFFF
4108
CALL SYSDELAY
CD BC 03
410B
DCRB
05
410C
JNZ X
C2 05 41
410F
POP PSW
F1
4110
POP D
D1
4111
POP B
C1
4112
RET
C9
MOV A,C
79
2501
STC
37
2502
CMC
3F
2503
RAL
17
2504
RAL
17
2505
RAL
17
2506
RAL
17
2507
ORI 20
F6 20
4100
4105
2500
DELAY
X
DISPLAY
Design lab II
14
2509
MOV H,A
67
250A
MVI L,00
2E 00
250C
MOV A,M
7E
250D
PUSH PSW
F5
250E
MVI A,85
3E 85
2510
OUT 19
03 19
2512
POP PSW
F1
2513
OUT 18
D3 18
2515
RET
C9
2000: 03(LED 0) 2100: 9F(LED 1) 2200: 25(LED 2) 2300: 0D(LED 3)
Design lab II
15
FURTHER CONSIDERATIONS As an extension of the given project, we were asked to interface the given system with stepper motors in order to physically simulate the elevator system designed. Owing to time constraints, this could not be implemented physically on the circuit. Nevertheless, we present how to interface stepper motors using 8255. AIM: To write a program to rotate the stepper motor clockwise/anticlockwise through definite number of steps. LOGIC: Initialize stack pointer and 8255 port A as output port. Out this control word to control word register. Give data CCh to accumulator to activate the stepper motor. Load the count in one of the register to determine number of steps. Loop1: Use RLC instruction in order to rotate clockwise. Out it to port A where we have connected stepper motor. Call delay subroutine. Decrement the count. Check the count for zero. If no, jump to Loop1. Otherwise, give data CCh to accumulator to activate the stepper motor. Load the count in one of the register to determine number of steps Loop2: Use RRC instruction in order to rotate anticlockwise. Out it to port A where we have connected stepper motor. Call Delay subroutine. Decrement the count. Check the count for zero. If no, jump to Loop2. Stop. Delay: Load one register with count. Decrement the register. Check for zero. If no, jump to step 2 of the delay. If yes, return to the main program.
Design lab II
16
ACKNOWLEDGEMENTS
The design of the elevator control mechanism was a challenging job. We would like to extend our gratitude to the concerned professor for providing us with valuable inputs and suggestions from time to time and making our task easier.
