PIN DIAGRAM OF DMA CONTROLLER FUNCTIONAL BLOCK DIAGRAM OF INTERNAL ARCHITECTURE OF . MSP Introduction. Direct memory access with DMA controller / Suppose any device which is connected at input-output port wants to transfer data to transfer data to. This allows CPU to communicate with Pin Diagram of During DMA cycles (i.e. when the is in the master mode) the Read/Write logic generates the.
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Data Bus D 0 -D 7: These are bi-directional tri-state signals connected to the system data bus. When CPU is introdcution control of system bus it can access contents of address register, status register, mode set register, and a terminal count register and it can also program, control registers of DMA controller, through the data bus.
During DMA cycles these lines are used to send the most significant bytes of the memory address from one of the. The four least significant lines A 0 -A 3 are bi — directional tri — state signals. In the idle cycle they are inputs and used by introductioj CPU to address the register to be loaded or read. In the Active cycle they output the lower 4 bits of the address for DMA operation. A 4 -A 7 are unidirectional lines, provide 4-bits of address during DMA service.
This signal is used to demultiplex higher byte address and data using external latch. This active high signal enables the 8-bit latch containing the upper 8-address bits onto the system address bus.
These are active low tri-state signals. These are active low bi-directional signals. In the active cycle IOR signal is used to access data from a peripheral and IOW signal is used to send data to the peripheral.
This active high signal clears, the command, status, request and temporary registers. After reset the device is in the idle cycle. It is used for requesting CPU to get the control of system bus. The active high Hold Acknowledge from the CPU indicates that it has relinquished control of the system bus.
These are used to indicate peripheral devices that the DMA request is granted. This is active high signal concern inroduction the completion of DMA service. MARK always occurs at all multiplies of cycles from the end of the data block. It is a tri-state, bi-directional, eight bit buffer which interfaces the to the system data bus.
In the slave mode, it is used to transfer data ccontroller microprocessor and internal registers of In master mode, it is used to send higher byte address A 8 -A 15 on the data bus.
Microprocessor – 8257 DMA Controller
During DMA cycles i. Each channel has two sixteen bit registers:.
It specifies the address of the first memory location to be accessed. It is necessary to load valid memory address in the DMA address register before channel is enabled.
N is number of bytes to be transferred. The value loaded into the low order 14 bits C 13 — C 0 of the terminal count register specifies the number of DMA cycles minus one before the terminal count TC output is activated. Therefore, for N number of desired DMA cycles it is necessary to load the value N-1 into the low order bits of the terminal count register. The most significant 2 bits of the terminal count register specifies the type of DMA operation to be performed.
It is necessary to load count for DMA cycles and operational code for valid DMA cycle in the terminal count register before channel is enabled. It consists of mode set register and status register. Mode set register is programmed dmw the CPU to controllrr whereas the status register is read by CPU to check which channels have reached a terminal count condition and status of update flag.
Least significant four bits of mode set register, when set, enable each of the four DMA channels. Most significant four bits allow four different options for the Pin Diagram of It is cleared by the RESET input, thus disabling all options, inhibiting all channels, and preventing bus conflicts on power-up.
Pin Diagram of | Block Diagram of | Mode Set Register | Status Register
As said earlier, it indicates which channels have reached a terminal count condition and includes the update flag described previously. The TC status bit, if one, indicates terminal count has been reached for that channel. TC bit remains set until the status register is read or the is reset. The update flaghowever, is not affected by a status read operation.
The update flag bit, if one, indicates CPU that is executing update cycle.
In update cycle loads parameters in channel 3 to channel 2. It resolves the peripherals requests. It can be programmed to work dam two modes, either in fixed mode or rotating priority mode. Your email address will not be published.
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