Purpose of the CTR DIV 8 block in a serial data path (counter divides by 8) In a system using a divide-by-8 counter labeled “CTR DIV 8” along with a control flip-flop, data output register, and a one-shot, what is the function of the divide-by-8 stage within the overall operation?
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AIt divides the clock frequency down to match the frequency of the serial data in.
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BThe divide-by-8 counter is triggered by the control flip-flop and clock, which then allows the data output register to begin storing the input data. Once all eight data bits are stored in the data output register, the data output register and the divide-by-8 counter trigger the one-shot. The one-shot then begins the process all over again.
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CThe divide-by-8 counter is used to verify that the parity bit is attached to the input data string.
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DIt keeps track of the eight data bits, triggering the transfer of the data through the output register and the one-shot, which then resets the control flip-flop and divide-by-8 counter.
Answer
Correct Answer: It keeps track of the eight data bits, triggering the transfer of the data through the output register and the one-shot, which then resets the control flip-flop and divide-by-8 counter.
Explanation
Introduction / Context:Divide-by-N counters are often used in serial interfaces to count received bits and control when a byte-wide register is latched or transferred. A “CTR DIV 8” suggests a modulo-8 counter, ideal for 8-bit (one byte) data framing in many systems.
Given Data / Assumptions:
- The counter divides by 8 (tracks 8 bit times).
- A control flip-flop, an output register, and a one-shot are present.
- Typical serial byte width is 8 bits (not counting start/stop/parity).
Concept / Approach:As serial bits arrive, the divide-by-8 counter increments one count per bit time. After eight counts, it signals “byte complete,” enabling a transfer or load of the parallel output register. A one-shot can generate a precise strobe or reset pulse to reinitialize the counter and control logic for the next byte.
Step-by-Step Solution:
1) Count incoming bits with CTR DIV 8: 0→7.2) When the count reaches 8, assert a terminal count signal.3) Use this signal to strobe the data output register and trigger the one-shot.4) One-shot pulse resets the control FF and the divide-by-8 counter to start the next frame.Verification / Alternative check:Observe timing: every eighth bit, a strobe occurs and the counter resets, yielding a repeating byte boundary.
Why Other Options Are Wrong:
- Dividing to match serial input rate (a): generic and not specific to byte framing.
- Option (b): too convoluted and implies the counter enables storage before counting all bits.
- Parity verification (c): parity requires XOR logic, not just a divide-by-8 counter.
Common Pitfalls:Confusing clock division with bit counting for framing; overlooking the role of a one-shot as a strobe/reset generator.
Final Answer:It keeps track of the eight data bits, triggering the transfer of the data through the output register and the one-shot, which then resets the control flip-flop and divide-by-8 counter.