Traffic Light Controller Using 8085 Microprocessor 26961

TRAFFIC LIGHT CONTROLLER Using 8085 Microprocessor SALIL MATHUR

T

his unique traffic light controller makes simple use of assembly language programming with Intel 8085 microprocessor. It permits accident-free control, as a separate set of signals has been assigned

to a particular direction. For instance, if one desires to move towards north, east or west from south, he is provided with a single light accomodating red, amber and green signals for the respective directions.

Software The program starts from memory location 6000. ADDR OP MNEMONICS INSTRUCTIONS CODE 6000

CD, 5061

CALL 6150

6003 6005 6007

3D, AA D3, 01 D3, 09

MVI A, AAH OUTPORT 01 OUTPORT 09

6009 600B 600D 600F

3E, FE D3, 00 D3, 08 CD, 1661

MVI A, FEH OUTPORT 00 OUTPORT 08 CALL 6116

6012 6014 6016 6018

3E, 16 D3, 00 D3, 08 CD, 0061

MVI A, 16H OUTPORT 00 OUTPORT 08 CALL 6100

601B 601D 601F 6021

6024 6026 6028 602A

3E, FF D3, 00 D3, 08 CD, 1661

3E, 29 D3, 00 D3, 08 CD, 0061

MVI A, FFH OUTPORT 00 OUTPORT 08 CALL 6116

MVI A, 29H OUTPORT 00 OUTPORT 08 CALL 6100

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This data calls a program on memory location 6150. Moving data AAH into port A(01) and port B(09) of IC 8255(1) and IC 8255(2) respectively, corresponds to all three signals indicating stop in east and west directions (Stage 1). This data alerts traffic in north (outport 08) and south (outport 00) directions of the next coming change. So a delay (five seconds) subroutine at 6116 has been called. Now, accomulator holds data 16H, which corresponds to two green signals from N to E, N to S and from S to W, S to N. However, N to W and S to E are red, as it will lead to an accident. Here a delay (30 seconds) subroutine at 6100 has been called to allow traffic to . This data allows introduction of amber signal prior to alternation of any signal, so that the moving and stopped vehicle can be alerted of any change change in signal. Use of delay subroutine again for 5 seconds allows the vehicle to judge and prepare for further signalling. The data allows diagonal movement from S to E (outport 00) and N to W (outport 08). The long delay (30 seconds) at 6100 has been called again to enable the signal at these outports to stay for

Consequently, the probability of confusion leading to an accident is reduced. Addition of an externally initiated trap for emergency provisions (for police, ambulance, fire brigade or VIPs) is a sophisticated feature, which can sometime (Stage 2). Now the traffic of east and west directions has to be allowed. So before that outports 00 and 08 have to be given alert signal for a delay of 5 seconds. Moving data AAH corresponds to all red in north and south directions.

602D 602F 6031 6033

3E, 2B D3, 00 D3, 08 CD, 1661

MVI A, 2BH OUTPORT 00 OUTPORT 08 CALL 6116

6036 6038 603A

3E, AA D3, 00 D3, 08

MVI A, AAH OUTPORT 00 OUTPORT 08

603C 603E 6040 6042

3E, FE D3, 01 D3, 09 CD, 1661

MVI A, FEH OUTPORT 01 OUTPORT 09 CALL 6116

6045 6047 6049 604B

3E, 16 D3, 01 D3, 09 CD, 0061

MVI A, 16H OUTPORT 01 OUTPORT 09 CALL 6100

604E 6050 6052 6054

3E, FF D3, 01 D3, 09 CD, 1661

MVI A, FFH OUTPORT 01 OUTPORT 09 CALL 6116

6057 5059 605B 605D

3E, 29 D3, 01 D3, 09 CD, 0061

MVI A, 29H OUTPORT 01 OUTPORT 09 CALL 6100

Moving data 29H allows diagonal movement from E to N and W to S for a delay of 30 seconds (Stage 4).

6060 6062 6064 6066

3E, 2B D3, 01 D3, 09 CD, 1661

MVI A, 2BH OUTPORT 01 OUTPORT 09 CALL 6116

6069

C3, 0060

JMP 6000

Now, traffic of north and south directions has to be allowed. So before that alert signal is given to traffic in east and west directions for 5 seconds. At this address, the control transfers to the beginning of the main program for repetition.

This data alerts traffic in east (outport 09) and west (outport 01) directions of the next coming change and a delay of 5 seconds has been called. Now, accomulator holds data 16H, which corresponds to two green signals from E to W, E to S and W to E, W to N. However, the W to S and E to N are red, as it may lead to an accident. Here delay of 30 seconds has been called to allow traffic movement (Stage 3). This data alerts traffic in east and west directions of the next coming change so a delay (5 seconds) subroutine at 6116 has been called.

(Continued on page 13)

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NOTE: TWO LEFT-MOST BITS ARE BEING NEGLECTED, AS ONLY SIX PORTS ARE USED FOR EACH DIRECTION.

Fig. 1: General view of the traffic control system.

Fig. 2: Bit position of the ports.

NOTE: PORTS 00 AND 01 ARE OF IC 8255(1) PORTS 08 AND 09 ARE OF IC 8255(2).

Fig. 3: Interface of LEDs to ports of ICs 8255. 12

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Fig. 4: Different stages showing traffic flow.

(Continued from page 11)

The data at location 6000 calls a program starting from memory location 6150 which is as follows: ADDR OP MNEMONICS INSTRUCTIONS CODE 6150 6152 6154 6156 6158 615B 615D 6160

3E, 80 D3, 03 D3, 0B 3E, FE 32, 5220 3E, 61 32, 5320 C9

MVI A, 80H OUTPORT 03 OUTPORT 0B MVI A, FEH STA 2052 MVI A, 61H STA 2053 RETURN

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This program moves data 80H into accumulator, so that the control ports 03 and 0B of IC 8255(1) and IC 8255(2) respectively are initialised. The address 61FE is stored at memory location 2052 (lower byte of address) and 2053 (higher byte of address).

Delay subroutine for 30 seconds: ADDR OP MNEMONICS INSTRUCTIONS CODE 6100 6102 6104 6106 6107 610A 610B 610E 610F 6112

06, 64 0E, FF 16, FF 15 C2, 0661 0D C2, 0461 05 C2, 0261 C9

MVI B, 64H MVI C, FFH MVI D, FFH DCR D JNZ 6106 DCR C JNZ 6104 DCR B JNZ 6102 RETURN

This delay subroutine uses three s B, C and D, where contents of B can be varied to change the time delay. Here 64H gives a delay of around 30 seconds. Total time delay =TD=T0+TL TL=Given T states x T (clock period) x count T0=Delay outside the loop. (Continued on page 14)

13

(Continued from page 13)

Delay subroutine for 5 seconds: ADDR OP MNEMONICS INSTRUCTIONS CODE 6116 6118 611A

06, 14 0E, FF 16, FF

MVI B, 14H MVI C, FFH MVI D, FFH

This subroutine provides a delay of around 5 seconds. Thus, the amber alert signal stays on

be remote-controlled also.

Emergency provision At the program starting from memory location 6150, we have stored 61FE at locations 2052 and 2053, respectively. This is for emergency provision.

MNEMONICS INSTRUCTIONS

61FE 6200 6202 6204 6206 6208 620A 620C 620E 6210 6212 6214 6216 6219 621B 621D 6220 6221 6224 6226 6228 622A 622C

MVI D, 30H MVI A, 80H OUTPORT 03 OUTPORT OB MVI A, AAH OUTPORT 00 OUTPORT 01 OUTPORT 08 OUTPORT 09 MVI C, 80H MVI A, FFH OUTPORT 02 CALL 6280 MVI A, 00H OUTPORT 0A CALL 6280 DCRC JNZ 6212 MVI A, 00H OUTPORT 00 OUTPORT 01 OUTPORT 08 OUTPORT 09

14

15 C2, 1C61 0D C2, 1A61 05 C2, 1861 C9

DCR D JNZ 611C DCR C JNZ 611A DCR B JNZ 6118 RETURN

Whenever the trap is externally triggered, the control goes into 0024H in monitor program where it gets signal of jumping to location 2052H. Thereafter, the control transfers to address 61FE which contains the emergency subroutine. The trap signal can be initiated through a push-

ADDR OP CODE 16, 30 3E, 80 D3, 03 D3, 0B 3E, AA D3, 00 D3, 01 D3, 08 D3, 09 0E, 80 3E, FF D3, 02 CD, 8062 3E, 00 D3, 0A CD, 8062 0D C2, 1262 3E, 00 D3, 00 D3, 01 D3, 08 D3, 09

611C 611D 6120 6121 6124 6125 6128

Here at 61FE, a pulse train of sound wave for fixed interval, corresponding to desired frequency is given at port C (02,0A) of IC 8255 for 45 seconds, after which the control transfers to the main program.

622E 6230 6232 6234 6236 6239 623B 623D 623F 6242 6243 6246 6247 624A

0E, FF 3E, FF D3, 02 D3, 0A CD, 8662 3E, 00 D3, 02 D3,0A CD, 8662 0D C2, 3662 15 C2, 0062 C3, 0060

for this time period. The control shifts to the main program when encountered with return statement.

button switch. Practical implementation of the above concept is feasible using SCRs and triacs as relays, which control the set of bulbs for a particular stage. These solidstate relays are triggered by signals from different ports of the microprocessor.

MVI C, FFH MVI A, FFH OUTPORT 02 OUTPORT 0A CALL 6286 MVI A, 00H OUTPORT 00 OUTPORT 0A CALL6286 DCR C JNZ 6236 DCR D JNZ6200 JMP6000

Blinking lights at each port are achieved by giving data of red and no signal, for small times, using the two delay subroutines at: ADDR OP CODE MNEMONICS 6280 6282 6283 6286 6288 6289 628C

06, FF 05 C2, 8262 06,80 05 C2, 8862 C9

MVI B, FFH DCR B JNZ6282 MVI B, 80 DCR B JNZ 6288 RETURN

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