Dma Controllers

Step 1: Understanding DMA Controller and Master Mode.
The 8237 DMA (Direct Memory Access) controller is used for memory-to-memory, I/O-to-memory, or memory-to-I/O data transfers. In Master Mode, the DMA controller controls the bus and performs the data transfer without CPU intervention.

Step 2: Evaluate each option.
- **Option A:** The signals Input Output Read and Input Output Write are kept in tri-state. This statement is incorrect. In Master Mode, these signals are not kept in tri-state, as the DMA controller takes control of them during the transfer.

- **Option B:** The signals Memory Read and Memory Write are kept in tri-state. This statement is correct. The memory-related signals are in tri-state during DMA operation, allowing the DMA controller to access memory without interference.

- **Option C:** The signals Input Output Read, Input Output Write, Memory Read, and Memory Write may all be used as per the data transfer requirement. This statement is incorrect. While the DMA controller can use these signals, it only uses the appropriate ones as per the data transfer mode (I/O or memory transfer).

- **Option D:** The data transfer can be terminated by sending low End of Process (EOP) from outside, also. This statement is correct. The transfer can be stopped externally by sending a low End of Process (EOP) signal, allowing for controlled termination of the transfer.

Step 3: Conclusion.
The correct statements are (B) and (D). Therefore, the correct answer is option (2).