8085 Applications

The 8085 Applications

Measurement of Voltage/Current

For measuring voltage/current we need to interface ADC 0808 with 8085 using 8255. Let us use port A of 8255 for transferring digital data output of ADC to the CPU and port C for control signals.

Assume that an analog input is present at I/P2 of the ADC and a clock input of suitable frequency is available for ADC.

Since the analog input I/P2 is used and therefore address pins A,B,C should be 0,1,0 respectively to select I/P2.

The OE and ALE pins are already kept at +5V to select the ADC and enable the outputs.

Port C upper acts as the input port to receive the EOC signal while port C lower acts as the output port to send SOC to the ADC.


This Configuration is shown in figure below


The 8255 control word is written as follows:

D7 D6 D5 D4 D3 D2 D1 D0

1 0 0 1 1 0 0 0 = 98H


The required ALP is as follows: MVI A, 98h ;initialize 8255 as OUT CWR ;discussed above. MVI A, 02h ;Select I/P2 as analog OUT Port B ;input. MVI A, 00h ;Give start of conversion OUT Port C ; pulse to the ADC MVI A, 01h OUT Port C MVI A, 00h OUT Port C

WAIT: IN Port C ;Check for EOC by reading port C upper RCR ;rotating through carry

JNC WAIT ;In no EOC, then check again IN Port A ;If EOC, read digital equivalent in A HLT ;Stop.

Measurement of Frequency

To evaluate frequency, the number of cycles/seconds has to be determined.

The signal input from the pulse generator is applied to SID line of the 8085. The RIM instruction reads the SID line and stores it in the 7th bit of accumulator.

The program detects the rising edge and subsequent falling edge of the signal. Once detected, it increments the count in HL pair, which is initialized to zero at the beginning. This way number of pulses is counted till the timer generates an interrupt to the processor.

The maximum delay produce by 8253 timer is 1/23 of second. The HL pair has number of pulses counted for 1/23 of second. Therefore, the content of HL pair is multiplied by 23 which gives total number of pulses per second.

The interrupt to processor is given through RST 5.5 line.

The Hardware configuration is shown below

The interrupt mask required is

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 1 1 1 1 0 = 1E

The CWR of timer required is

D7 D6 D5 D4 D3 D2 D1 D0

0 0 1 1 0 0 0 0 = 30H

The Program is given by

MVI A,30 ;Control word for timer

OUT CWR ;Port Addres of CWR of Timer

MVI A,FF ;Move LSB of the count to counter0

OUT CONT0 ;Port address of counter 0

MVI A,FF ;Move MSB of count to counter0

OUT CONT0 ;Port address of counter0

LXI H,0000 ;Clear HL pair for pulse count

EI ;Enable Interrupt

MVI A,1E ;Set RST5.5 SIM ;Set interrupt mask

Nohigh: RIM ;Identify low to high transition

ANI 80

CPI 80 ;Compare with 80

JC Nohigh ;If no transition look again

Nolow: RIM ;Identify high to low transition

ANI 80

CPI 80

JZ Nolow ;If no transition look again

INX H ;If transition completes increament pulse count

SHLD 4200 ;Store pulse count at 4200

JMP Nohigh ;Repeat for more pulse count

The ISR of RST5.5

002C: JMP 4300 ;jump to specific address

4300: LHLD 4200 ;Get the count of pulses in HL pair

XCHG ;Copy the count in DE pair

LXI H,0000 ;Clear HL pair

MVI B,17 ;Initialize B to 17H(23D)

Repeat: DAD D ;Add HL pair and DE pair

DCR B ;Decrement B

JNZ Repeat ;Multiplication by repeated addition

SHLD 4500 ;Store HL pair in 4500 and 4501

LDA 4501 ;start packed to unpacked conversion

ANI F0 ;AND to get the MSD

RRC ;Rotate to get the digit in right position

RRC

RRC

RRC

STA 4600 ;Store it at 4600

LDA 4501

ANI 0F ;AND to get LSD


LDA 4500 ;Get Lower significant two digits

ANI F0 ;AND to get the MSD

RRC ;Rotate to get the digit in right position

RRC

RRC

RRC


LDA 4500

ANI 0F ;AND to get LSD


LXI H,4600 ;Call Display routine to Display result

MVI A,03

MVI C,09 ;Segment Address

CALL 0005 ;Display Routine

HLT

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8085 Applications