The document discusses serial input/output (I/O) data transmission using the 8085 microprocessor. It describes how the serial input data (SID) pin is used to accept serial 1-bit data under software control during a RIM instruction. It also describes how the serial output data (SOD) pin is used to transfer 1-bit data under software control during a SIM instruction. It provides an example program that generates a 1 kHz square wave on the SOD pin by toggling between logic 0 and 1 using different accumulator values in the SIM instruction and a delay subroutine.

1. Microprocessor & Microcontroller - I
T.E Sem V (Rev)
Prof. Nitin Ahire
XIE, Mahim

2. 8085 serial I/O Data transmission
• Serial communication is useful for data transfer
between two points serially.
• SID (serial input data) used to accept serial 1 bit
data under software control when a RIM
instruction is executed the SID pin data is loaded
in bit D7 of Accumulator
• SOD (serial output data) used to transfer 1 bit
data under software control when a SIM
instruction is executed the SOD pin is set or reset
depending on D7 and D6 bit of Accumulator

3. 8085 serial I/O Data transmission
SOD
GND GND
8085
Serial I/P
Serial
Device
SID Serial 0/P

4. 8085 serial I/O Data transmission
instruction SIM
• To do the data transmission (TXE) 8085 uses SIM
instruction
• The SIM instruction uses the accumulator content as
shown above
• The sequence of instructions required
• Logic 0 MVI A,40h
SIM
& for
Logic 1 MVI A, C0h
SIM
SOD SDE M’ 6.5M’ 7.5MSER 7.5X M’ 5.5
SOD pin
Serial Data enable

5. 8085 serial I/O Data transmission
• Write a program to generate a square
wave of 1 KHZ using SOD pin of 8085.
Sol: Time period=1/f =1ms
Ton + Toff = 1ms ( Ton=0.5ms )
Delay required = 0.5ms

6. 8085 serial I/O Data transmission
• main program
UP: MVI A,C0H ; for logic 1
SIM
CALL DELAY ; (0.5MS)
MVI A,40H ; for logic 0
SIM
CALL DELAY ; (0.5 MS)
JMP UP

7. 8085 serial I/O Data transmission
• DELAY calculation considering 8 bit prog.
• Td = [17+[ {count} X 14 ] -3] T
0.5ms = [17+[{count}X14]-3] 0.33ms
So count= (104)D=(68)h
delay program Delay Subroutine
LOOP: MVI C,68H
DCR C
JNZ LOOP
RET

8. 8085 serial I/O Data transmission
SOD
GND GND
8085
Square Wave of 1KHZ Freq.