--- title: "MBI block diagram, advantages and DMA" subject: "Instrumentation II" chapter: 1 key: "semester_5/instrumentation_ii:mbi-block-advantages-dma" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/mbi-block-advantages-dma site: BCT Engineering --- # MBI block diagram, advantages and DMA Instrumentation II · Chapter 1: Microprocessor Based Instrumentation System - Asked in: 2071 Shrawan, 4+2+2 marks - Video: [Direct Memory Access - DMA - Simplified Explanation](https://www.youtube.com/watch?v=wi-po2SesoE) — Mohammed Adil - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/mbi-block-advantages-dma - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-1 ## Question Draw and explain the block diagram of microprocessor based instrumentation system. Also list out advantages of implementing an MBI system. Explain briefly the concept of DMA. ## Short answer MBI system: sensor, conditioner, ADC, microprocessor with ROM/RAM and I/O for display/keypad, DAC/driver/actuator, serial link. Advantages: programmable, high accuracy, multi-channel, alarms, logging. DMA transfers data blocks directly between device and memory using HOLD/HLDA, bypassing CPU for fast moves. ## Answer #### Block diagram of an MBI system ```text Sensor -> Signal conditioner -> S/H -> ADC --+ ^ v | +------------------+ PLANT | Microprocessor |<-> ROM/RAM | | (CPU, I/O ports) |<-> Keypad, v +------------------+ Display, Actuator <- Driver <- DAC <----------------+ | Printer, +-> Serial link ``` **Sensor** converts the measured quantity to an electrical signal; the **signal conditioner** amplifies, filters and scales it; the **S/H and ADC** digitise it; the **microprocessor** with **ROM** (program) and **RAM** (data) processes the data; **I/O ports** connect keypad, display and printer; the **DAC, driver and actuator** apply the control action to the plant; a **serial link** connects to a supervisory computer. #### Advantages of MBI systems 1. Programmable, so functions are changed without hardware change. 2. Higher accuracy, linearisation and automatic calibration. 3. Automatic decision making, alarms and safety interlocks. 4. Many channels handled by one processor. 5. Data logging, display and remote communication. 6. Less wiring, lower cost, size and power, higher reliability. 7. Easy expansion and maintenance (self-test and diagnostics). #### DMA (Direct Memory Access) DMA transfers a block of data directly between an I/O device and memory without the CPU executing instructions for every byte. The DMA controller (e.g. 8237) requests the bus with **HOLD**, the CPU finishes its cycle, floats its buses and replies **HLDA**. The controller then generates the memory address and the read/write signals and transfers bytes at memory speed. After the count is finished, it releases HOLD and the CPU resumes. ```text Device --DREQ--> DMAC --HOLD--> CPU Device <--DACK-- DMAC <--HLDA-- CPU Device <==== data ====> Memory ``` DMA is used for fast block transfers such as ADC data acquisition and disk transfer. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main idea of DMA? A. Data moves between I/O device and memory without CPU executing instructions for each byte B. The CPU copies every byte using IN/OUT C. DMA only works with interrupts D. DMA replaces memory Answer: A. The DMAC takes over the bus and transfers blocks directly. (Key point: DMA concept) 2. What do HOLD and HLDA do? A. CPU sends HOLD to the device; DMAC replies HLDA B. DMAC requests the bus with HOLD; CPU floats its buses and replies HLDA C. HOLD is sent by the memory D. HLDA resets the DMAC Answer: B. HOLD is the request and HLDA the grant. (Key point: HOLD and HLDA) 3. DMA is best suited for which task? A. Reading one keypress B. Slow single-byte status checks C. Fast block transfers like ADC data acquisition and disk transfer D. Controlling one LED Answer: C. Block transfers benefit from DMA speed. (Key point: DMA use) 4. Which is an advantage of MBI systems? A. Needs more hardware logic B. Cannot be modified C. Cannot log data D. One processor handles many channels with lower cost and wiring Answer: D. Multiplexing and programmability reduce cost and wiring. (Key point: MBI advantage) ## Related in Instrumentation II - [MBI block diagram and advantages in industry](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-advantages) — Instrumentation II, chapter 1 - [Rationale for microprocessor; open-loop MBI; DMA](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Arationale-open-loop-dma) — Instrumentation II, chapter 1 - [Features of microprocessor based instrumentation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-features) — Instrumentation II, chapter 1, asked 4× - [Types of microprocessor based instrumentation systems](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-types) — Instrumentation II, chapter 1 - [MBI block diagram and basic features](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-features) — Instrumentation II, chapter 1, asked 4× - [DMA concept; ROM/RAM interface at 4000H](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adma-memory-interface-4000h) — Instrumentation II, chapter 1 ## Related in other subjects - [Instrumentation system with block diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Ainstrumentation-system) — Basic Electronics Engineering, chapter 7, asked 3× - [Microprocessor based system and bus organization](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Amp-based-system-bus-organization) — Microprocessor, chapter 1, asked 5× - [DMA controller block diagram and transfer](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Adma-controller) — Computer Organization and Architecture, chapter 7, asked 6× - [Microprocessor-based transmission line protection](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Amicroprocessor-line-protection) — Switchgear and Protection, chapter 8, asked 2×