Bangladesh Bank; Assistant Maintenance Engineer Written Exam: 2011প্রশ্ন ও সমাধান

SPI (Serial Peripheral Interface) is a synchronous, full-duplex serial communication protocol developed by Motorola for short-distance chip-to-chip communication (e.g. microcontroller to flash memory, sensors, ADC, RTC).

How it works: SPI uses a master-slave architecture with 4 signal lines:

• SCLK — Serial Clock, generated by the master.
• MOSI — Master Out, Slave In.
• MISO — Master In, Slave Out.
• SS/CS — Slave/Chip Select, one dedicated line per slave (active low).

graph LR
  M[Master] -- SCLK --> S1[Slave 1]
  M -- MOSI --> S1
  S1 -- MISO --> M
  M -- SS1 --> S1
  M -- SCLK --> S2[Slave 2]
  M -- SS2 --> S2

Data shifts in both directions simultaneously on every clock pulse (full-duplex), and each slave is individually addressed through its own chip-select line rather than a shared bus address, unlike I2C.

Advantages over a parallel interface:

Aspect	SPI (serial)	Parallel interface
Wires needed	Few (4 + 1 per slave)	Many (one per data bit + control lines)
Speed over distance	Better (less crosstalk/skew)	Degrades quickly with distance
Cost / PCB complexity	Lower	Higher (more pins, more routing)
Duplex mode	Full-duplex	Usually half-duplex, or needs extra lines
Clock synchronization	Simple (one shared clock)	Complex (bit skew across many lines)

Takeaway: SPI trades a wide parallel bus for a simple, fast, full-duplex serial link — ideal for connecting a microcontroller to nearby peripheral chips with minimal pin count.

A computer system is made of interacting elements that together accept input, process it, and produce output. The five core elements are:

• Hardware: Physical components — input devices (keyboard, mouse, scanner), processing/memory hardware (CPU, RAM), output devices (monitor, printer), secondary storage (HDD, SSD, pen drive).
• Software: Instructions driving the hardware — system software (OS, e.g. Windows, Linux) and application software (MS Word, browsers).
• Data: Raw facts/figures fed into the system to be processed into information.
• People: End users, operators, programmers, and system analysts who interact with and maintain the system.
• Procedures: Documented rules/steps describing how to operate the system correctly and consistently.

graph TD
  Data --> CPU((CPU / Processing))
  Hardware --> CPU
  Software --> CPU
  CPU --> Output
  People -.operate.-> CPU
  Procedures -.govern.-> CPU

Characteristics of a computer system: Speed (executes millions of instructions per second), Accuracy (near-zero error given correct input/logic), Diligence (no fatigue, consistent over long runs), Storage (retains large volumes of data), Automation (runs unattended once programmed), Versatility (handles diverse tasks — calculation, graphics, communication).

Takeaway: A computer system is more than hardware — Hardware, Software, Data, People, and Procedures must all work together; removing any one element breaks the system.