Question

Frequency range of 8257 is

• A. \( \text{500Hz to 3MHz} \)
• B. \( \text{250Hz to 3MHz} \)
• C. \( \text{500Hz to 2MHz} \)
• D. \( \text{250Hz to 2MHz} \)

Hint:

For specific integrated circuits (ICs) like the 8257 DMA controller, 8255 PPI, 8259 PIC, etc., it's often helpful to remember their key specifications, including their operating frequency ranges. These chips are fundamental components in early microprocessor systems, and their characteristics are part of the core knowledge in digital electronics and microprocessor architecture.

Answer 1

The Correct Option is B

To solve this problem, let's dive into the details of how the 8257 DMA (Direct Memory Access) controller works, specifically its frequency range.

1. What is a DMA Controller?

A DMA controller is a hardware component that allows peripherals (like sensors or storage devices) to communicate with memory directly, without involving the CPU. This significantly speeds up data transfer, as it bypasses the CPU for large amounts of data. The 8257 DMA controller is commonly used for such tasks in computer systems.

2. How Does the 8257 DMA Work?

The 8257 DMA controller takes over the bus and manages data transfers between memory and I/O devices. It uses a clock frequency to determine how fast data is transferred. The controller can operate at different frequencies depending on the system's requirements. These frequencies define how fast the controller operates and affect how quickly data can be transferred between memory and the peripheral device.

3. Frequency Range of the 8257 DMA Controller:

The frequency range for the 8257 DMA controller refers to the minimum and maximum clock frequencies at which the controller can function effectively. For the 8257, this range is 250 Hz to 3 MHz. Let's break down this range:

• 250 Hz: This is the lower bound of the frequency range. It means the DMA controller can operate with a clock frequency as low as 250 Hz. At this frequency, the controller is quite slow, and it transfers data at a much lower rate.
• 3 MHz: This is the upper bound of the frequency range. It indicates that the controller can work with a clock frequency as high as 3 MHz, making it suitable for faster data transfers in more high-speed applications.

4. Explanation of the Options:

- Option 1: "500Hz to 3MHz" – This is incorrect because the 8257 DMA starts at 250 Hz, not 500 Hz. The lower bound is not 500 Hz. 
- Option 2: "250Hz to 3MHz" – This is correct. As explained, the 8257 DMA controller can operate effectively in the range of 250 Hz to 3 MHz. This is the actual operating frequency range of the 8257 DMA controller. 
- Option 3: "500Hz to 2MHz" – This is incorrect. The 8257 DMA controller supports a maximum frequency of 3 MHz, not 2 MHz. Also, the lower bound of the frequency range is 250 Hz, not 500 Hz. 
- Option 4: "250Hz to 2MHz" – This is incorrect. While the lower bound is correct (250 Hz), the upper bound is wrong. The 8257 supports up to 3 MHz, not 2 MHz.

5. Why This Matters:

Understanding the frequency range of the 8257 DMA controller helps in selecting the appropriate clock for applications that need fast data transfers. If you need to transfer large chunks of data quickly, a higher frequency, closer to 3 MHz, would be used. If the data transfer speed is less critical, a lower frequency (such as 250 Hz) can be used to save power or reduce system load.

6. Final Answer:

The correct frequency range of the 8257 DMA controller is 250Hz to 3MHz.