This document discusses serial and parallel data transfer modes in microprocessors. It focuses on the 8085 microprocessor. There are two main modes: parallel I/O mode where the 8085 communicates directly with I/O devices using its full data bus, and serial I/O mode where it uses a converter and single data line. Serial I/O involves asynchronous or synchronous transmission formats, with asynchronous using start and stop bits to delineate characters. The 8085 has two pins, SOD and SID, for software-controlled serial I/O using the SIM and RIM instructions to output and input single bits of serial data.

1. MICROPROCESSOR 8085
LECTURE 26
SERIAL AND PARALLEL DATA TRANSFER
PROF. SANDIP DAS

2. PARALLEL I/O MODE
8085 MPU I/O Device
0
1
1
0
0
1
SERIAL I/O MODE
8085 MPU
Parallel to
Serial
Converter
0
1
1
0
0
1
100110
To I/O
Device

3. SERIAL I/O MODE
The basic concepts concerning the Serial mode can be classified
into the following:
• Interfacing requirements
• Alphanumeric codes
• Transmission format
• Error checks in Data Communication
• Standards in Serial I/O
• Software vs Programmable Hardware approaches

4. INTERFACING REQUIREMENTS
8085 MPU Serial
Peripheral
Trans
mitReceiv
e
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• The microprocessor identifies the peripheral through
a port address and enables it using the Read or Write
control signal.
• The primary difference between parallel I/O and
Serial I/O is in the number of lines used for data
transfer-Parallel I/O uses the entire data bus and
Serial I/O uses one data line.

5. TRANSMISSION FORMAT
• Synchronous Transmission
• Asynchronous Transmission
SYNCHRONOUS TRANSMISSION
• In Synchronous format, a receiver and a transmitter are synchronized
• A block of characters is transmitted along with the synchronization
information.
Syn
c
Syn
c
Data
TimeStart
Transmi
tter
Receiver
Clock

6. ASYNCHRONOUS TRANSMISSION
• Asynchronous format is character oriented. Each character carries the
information of the Start and Stop bits.
• When no data are being transmitted, a receiver stays HIGH at logic 1, called
Mark; logic 0 is called as space.
• Transmission begins with one Start bit (LOW), followed by character and one
or two Stop bits (HIGH). This is called as framing.
D
0
D
1
D2 D3 D4 D5 D6 D7
TimeStart
Transmi
tter
Receiver
Start
Stop
bits
Marking
ASCII
Characters

7. 8085 SERIAL I/O LINES: SOD AND SID
• 8085 has two pins for software controlled I/O- SOD and SID.
• Data transfer is controlled through two instructions: SIM and RIM.
SERIAL OUTPUT DATA (SOD)
MVI A,C0 Set D7, D6 in the accumulator=1
SIM Output D7, rather transfer 1 to I/O device
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
SOD SDE XXX R 7.5 MSE M 7.5 M 6.5 M 5.5
1= Enable
SOD
Serial Output
Data
8085 MPU I/O Device
SOD
SI
D
MVI A,40 Set D7=0, D6 in the accumulator=1
SIM Output D7, rather transfer 0 to I/O device

8. SERIAL INPUT DATA (SID)
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
SID I7.5 I6.5 I5.5 IE M 7.5 M 6.5 M 5.5
Serial Input data
Interrupt Status
Instruction RIM is used to input Serial data through the SID line.