How does the program test whether a byte has odd parity?

ORA A sets the flags without changing A; P = 1 means even parity, so JPO jumps for odd parity

CPI 51H sets P = 1 for odd parity, then JPE

ANI 01H tests bit D0; if it is 1 the byte has odd parity

RRC moves each bit into carry and JC counts the 1s

For an even-parity byte, which instructions clear bit D5 and set bit D3, and what does 03H become?

ANI 0DFH then ORI 08H; 03H becomes 0BH

ORI 20H then ANI 08H; 03H becomes 08H

ANI 08H then ORI 0DFH; 03H becomes DFH

ANI 0DFH then ORI 08H; 03H becomes 23H

Why is CPI 51H / JZ DONE placed before the parity test?

So the program stops when it reads the end marker 51H, without transferring it

Because CPI is needed to set the parity flag

So that 51H is transferred and then the program stops

Because 51H has even parity and must be modified first

2069 Poush · 8 marks

8085 ALP: odd parity transfer with bit change

Short answer

Check for end marker 51H (not transferred). Use ORA A and JPO to detect odd parity: copy byte unchanged if odd; else clear bit D5 (AND DFH) and set bit D3 (OR 08H) then store. Example: 07H stays 07H, 03H becomes 0BH.

Write a program in 8085 to transfer bytes of data with odd parity from location 9205H to A200H, else transfer the data by clearing bit D5 and setting bit D3. The end of the data bytes is indicated by 51H in the data.

A byte has odd parity when it contains an odd number of 1s. After ORA A the 8085 parity flag P = 1 for even parity, so JPO (jump if parity odd) detects odd parity. The end marker 51H is tested first and is not transferred.

Algorithm

HL → 9205H (source), DE → A200H (destination).
Read a byte; if it equals 51H, stop.
Test parity (ORA A). If odd, store it unchanged.
If even, clear D5 (AND with DFH = 1101 1111) and set D3 (OR with 08H), then store.
Advance both pointers and repeat.

        LXI  H,9205H      ; HL = source pointer
        LXI  D,0A200H     ; DE = destination pointer
NEXT:   MOV  A,M          ; get data byte
        CPI  51H          ; end of data?
        JZ   DONE         ; yes -> stop (51H is not transferred)
        ORA  A            ; set flags, P=1 for even parity
        JPO  STORE        ; odd parity -> transfer unchanged
        ANI  0DFH         ; even parity: clear bit D5
        ORI  08H          ; and set bit D3
STORE:  STAX D            ; store byte at destination
        INX  H            ; next source byte
        INX  D            ; next destination location
        JMP  NEXT
DONE:   HLT

Example: 07H (three 1s, odd) is copied as 07H. 03H (two 1s, even) becomes 03H AND DFH = 03H, OR 08H = 0BH. 20H (one 1, odd) is copied as 20H.

✓ Answer checked by Claude Opus 5.5 (high effort)

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