Comparing RISC with CISC for a small battery-powered device, RISC is generally preferred because
Answer: C
Simplicity of decode is where the saving lies, and it shows up as both die area and switching energy. Code density is usually the CISC machine's advantage, which is why compressed instruction sets such as Thumb were introduced to claw some of it back.
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A microcontroller differs from a microprocessor chiefly in that it
Answer: D
The processor core may be identical; what makes it a microcontroller is having flash, RAM, timers, converters and serial ports in the same package. That integration is what lets a product be built round a single device and a handful of passives.
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Three of the following are normally integrated on a microcontroller. The exception is
Answer: A
Correct answer: a hard disk controller
A microcontroller integrates what an embedded application needs on one chip: flash, RAM, timers, converters, serial ports and general purpose I/O. A hard disk controller belongs to a class of system a microcontroller is not built for - embedded storage is flash or an SD card over SPI, and the mass-storage interface would dwarf the rest of the device.
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A design requires a 32-bit core, 2 MB of flash, an Ethernet MAC and a Linux kernel. The appropriate device class is
Answer: B
A general purpose kernel needs a memory management unit and tens of megabytes of RAM, which puts the design beyond any microcontroller. An FPGA with a soft core could be made to work but would cost far more in parts and effort for a standard requirement.
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Which memory type retains its contents without power and can be erased electrically in blocks?
Answer: C
Block erasure is the distinguishing feature: byte-erasable non-volatile memory is EEPROM, and flash trades byte granularity for much higher density. It is why program memory is flash and small calibration stores are often EEPROM.
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SRAM is preferred to DRAM for the small on-chip memory of a microcontroller because it
Answer: D
A refresh controller and the special capacitor process DRAM needs are both unwelcome on a logic die. SRAM costs six transistors a bit against DRAM's one and a capacitor, so it is far less dense, which is why it is used in kilobytes and DRAM in megabytes.
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The memory map of a microcontroller is
Answer: A
Reading a datasheet's memory map tells you where flash, RAM and each peripheral's registers appear, which is the first thing needed to write any driver. Two devices with the same core and different maps need different code.
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A processor with a 16-bit address bus can address at most
Answer: B
Two to the sixteenth is 65536, so 64 kibibytes if each location holds a byte. Extending the reach beyond that without more address lines needs bank switching, which is why the 8-bit generation was full of paging schemes.
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A device has 20 address lines and an 8-bit data bus. Its directly addressable memory is
Answer: C
Correct answer: 1 MB
\[ 2^{20} = 1{,}048{,}576 \] addressable locations, each holding one byte on an 8-bit data bus, so 1 MB. The data bus width sets the size of each location, and the number of address lines sets how many there are - multiplying the two, as the 8 MB option does, confuses bits with bytes.
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The width of the data bus of a processor determines
Answer: D
Address lines fix the reach and data lines fix the throughput per access, and the two are independent: an 8-bit machine with twenty address lines reaches a megabyte one byte at a time. Confusing the two is the commonest slip in bus questions.
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