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In DMA as the name suggest the memory can be accessed directly by i/o module. Thus overcome the drawback of programmed i/o and interrupt driven i/o where the CPU is responsible for extracting data from the memory for output & storing data in memory for input. DMA provids different information.
i) which operation (read/write) to be performed.
ii) The address of i/o device which is to be used.
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∙ 16y ago
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Is dma controller is processor or controller?
processor
Is it possible to use a dma controller if the system does not supports the interrupts?
You'd have to use DMA with polling, and thats usually not supported
What 8257 chip means?
The 8257 is a three channel DMA controller.
How does DMA work?
There are signals DACK, DRQ, and TC. When a peripheral wants to move a byte or 2 bytes into memory (is dependent on whether 8 bit or 16 bit DMA channel is in use -- 0,1,2,3 are 8-bit, 5,6,7 are 16-bit), it issues DRQ. DMA controller chats with CPU and after some time DMA controller issues DACK. Seeing DACK, the peripheral puts it's byte on data bus, DMA controller takes it and puts it in memory. If it was the last byte/word to move, DMA controller sets up also TC during the DACK. When peripheral sees TC, it is possible it will not want any more movements,
What is the future type of external memory?
If you mean after external hard drives, probably am 80 GB credit card. MSM9841 and MSM9842 offers two types of memory interface: interface when DMA controller is used (16-bit bus) that memory interface is through DMA controller; interface without DMA controller that memory interface (16-bit bus) is through CPU.
What is the use of Intel 8257 microprocessor?
Its a Programmable Direct Memory Access (DMA) controller.
What is busmastering?
bus mastering is a feature supported by many bus architectures that enables a device connected to the bus to initiate transactions. Also called "First-party DMA", to contrast it with Third-party DMA, the situation where the system DMA controller is actually doing the transfer.
When does dma controller take control of the bus?
When a DMA module takes control, the processor will communicate with hilario and mark tan with their super friends. they will do their best to kill bernard aguila and his brother roshan to get the AEGIS OF IMMORTAL ...
Why DMA controller data transfer is faster?
The direct memory access or DMA mode of data transfer is the fastest amongst all the modes of data transfer.In this mode ,the device may transfer data directly to/from memory without any interference from the CPU.The device requests the CPU through a DMA controller to hold its data,address and control bus so that the device may transfer data directly to/from memory.
What is burst mode and cycle stealing mode?
The DMA controller can be used to steal memory cycles from the processor. Hence this interweaing technique is called cycle stealing The DMA Controller may be Given exclusive access main memory to transfer the block of data without interruption this is known as block or burst mode
Which direct memory access channel is used for the floppy controller?
From http://www.brainbell.com/tutors/A+/Hardware/Direct_Memory_Access_DMA.htm "DMA channels use the same rules as IRQs. Just as with the 8259 chip, DMA availability soon became a problem because an insufficient number of channels was available. A second DMA chip was added for 286-based computers. Just like the second IRQ chip, these two are cascaded, allowing a total of eight DMA channel assignments (usually referred to simply as DMA channels). The floppy disk drives on all computers use DMA channel 2."
Basic DMA operation and 8237 DMA Controller?
In the 8085, DMA (Direct Memory Access) is controlled with HOLD and HLDA. The HOLD signal is a request to release the bus. The HLDA signal is the 8085's acknowledgement of that request. HLDA means that the 8085 will release the bus in one half clock cycle, i.e. at the end of T3. The 8085 will remain in that hold state until HOLD is released, at which point it will take control of the buses again. The HOLD'ing device has complete control and can access any memory or I/O. Often, the 8237 DMA controller is used to provide sequencing of the operation. The 8237 DMA controller interfaces between up to four peripheral devices and the 8085. It provides an address register for each device so that the device does not need to do so. The device only needs to indicate that a byte of data is available, or is required, and the 8237 will take care of storing or fetching the byte.
