T1SOL051ol - Embedded Controller Hardware Design...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Embedded Controller Hardware Design 051olx024ol Mid-term Solutions 1 1) What is an “open drain” output and what is it used for? An open drain is a type of MOS logic output that has a pull down N-channel transistor, and no internal pull-up device. The designer must include an external device (typically a resistor between the output and V+) which will pull the output to a logic high level when the open drain output is off. It is used for “wire-OR” logic. 2) What is the difference between setup and hold time? Setup time is the amount of time a signal must be valid before a clock transition, and hold time is the amount of time a signal must remain valid and stable after the clock transition. 3) How is a Flash EPROM programmed and erased? Flash EPROM is programmed and erased electrically, by trapping and removing charge from an electrically isolated, floating transistor gate. An entire block of memory, or the whole chip must be erased at one time prior to programming. 4) What is the value Vt for 74HCTxx logic? TTL compatible logic of ANY kind (including 74HCTxx) has the same threshold as TTL logic: ~1.5 volts, regardless of the supply voltage. Not the same as standard CMOS logic (74HCxx), which has a threshold of ~half the power supply voltage, ~2.5 volts for a 5 volt supply. The logic threshold (Vt) is the voltage which defines the decision point for a logic input to distinguish between logic one and logic zero. 5) What is noise margin, and is a larger magnitude better or worse? The noise margin is the amount of noise that can be added to a valid logic output voltage without exceeding the specified input voltage requirement for the same logic level. e.g.: Voh min - Vih max for logic high, and Vil max - Vol min for logic low. When the margin is negative, it means that the logic levels are not compatible. (Noise may be AC or DC offset error added to the signal.) More positive values are better than more negative values. 6) What is metastability and when does it occur? Metastability is when a clocked logic device does not reach a valid and stable logic 0 or 1 state in the specified time. It occurs only rarely, but it is caused by a violation of either the setup or hold time of signal. 7) Why is non-volatile memory used for embedded program storage? Non-volatile memory does not lose its contents when power is removed. Since most embedded systems do not have disk drives, the programs are usually stored in non- volatile semiconductor memory like Flash, EEPROM or UV EPROM. 8) What is asymmetrical delay, and why does it occur?
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

T1SOL051ol - Embedded Controller Hardware Design...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online