PROGRAMMABLE DMA CONTROLLER - INTEL 8257
It is a device to transfer the data directly between IO device and memory without through the CPU. So it performs a high-speed data transfer between memory and I/O device.
The features of 8257 is,
The 8257 has four channels and so it can be used to provide DMA to four I/O devices
Each channel can be independently programmable to transfer up to 64kb of data by DMA.
Each channel can be independently perform read transfer, write transfer and verify transfer.
It is a 40 pin IC and the pin diagram is,
Functional Block Diagram of 8257:
The functional blocks of 8257 are data bus buffer, read/write logic, control logic, priority resolver and four numbers of DMA channels.
The functional block diagram of 8257 is shown in fig.
Functional block diagram
Operating Modes of DMA 8257 ->>Page2