_______ is a DMA controller which has four independent channels, CH0 to CH3.

Explanation:

8237 DMA Controller

Definition: The 8237 is a Direct Memory Access (DMA) controller developed by Intel. It is used to transfer data directly between peripherals and memory without involving the CPU, thereby improving the efficiency of data transfer. The 8237 DMA controller has four independent channels, labeled CH0 to CH3, each capable of handling a separate I/O device or memory transfer operation.

Working Principle: The 8237 DMA controller operates by taking control of the system bus during data transfer operations. The process involves the following steps:

• Initialization: The CPU initializes the DMA controller by setting up the base address, count, and control registers for each channel.
• DMA Request: When a peripheral device needs to transfer data, it sends a DMA request to the 8237 controller on the appropriate channel.
• DMA Acknowledge: The DMA controller acknowledges the request and takes control of the system bus by asserting the HOLD signal to the CPU.
• Data Transfer: The DMA controller transfers data directly between the peripheral and memory. The transfer can be in burst mode or cycle stealing mode, depending on the configuration.
• Completion: Once the data transfer is complete, the DMA controller releases the bus by de-asserting the HOLD signal, allowing the CPU to regain control.

Features:

• Four independent channels (CH0 to CH3) for concurrent data transfers.
• Supports various modes of operation, including single transfer, block transfer, demand transfer, and cascade mode.
• Programmable base address and count registers for each channel.
• Supports 8-bit data transfer.
• Provides bus arbitration to manage control of the system bus between the CPU and DMA controller.