Direct memory access

It is possible to improve the performance of the hardware (hereafter called the MVP-9500) by providing interrupt facilities to signal completion of operation(s) or to request more data and also by moving data via direct memory access rather than under Z80 program control. These, and other refinements, were... 

CPU olf-load mechanisms such as Direct Memory Access (DMA)... 

Another feature of the bus is that it allows devices to bypass the processor and write their information directly into main memory. This feature is known as direct memory access, or DMA. Each type of bus has a different number of channels that can be used for DMA. If two devices are set to the same DMA channel, neither device will write information to memory correctly thus, neither device will work. 

In general, there are four main types of PC resources that you might need to be aware of when installing a new component interrupt request (IRQ) lines, memory addresses, direct memory access (DMA), and I/O addresses. 

Direct memory access (DMA) is a method used by peripherals to place data in memory without utilizing (or bothering) the CPU. As an example, a sound card can buffer music in memory while the CPU is busy recalculating a spreadsheet. The DMA peripheral has its own processor to move the data. It uses dead time on the ISA bus to perform the transfer. At the hardware level, DMA is quite complex, but the important feature to remember is that the transfer of data is accomplished without intervention from the CPU. 

DMA (direct memory access) A method of transferring information directly from a mass-storage device such as a hard disk or from an adapter card into memory (or vice versa), without the information passing through the processor. 

A. Direct Memory Access (DMA) channels allow a device to write directly to memory. Bus mastering allows devices to write directly to each other. See Chapter 5 for more information. 

PCI-interface The PCI-interface writes the data via direct memory access (DMA) into the PC-memory. The data transfer rate achieved is 85 MB/s which has to be compared with an expected data rate of 20 MB/s. 

Hardware. To employ the IDA, the user must supply a clock signal, a begin scan signal, and data acquisition hardware. The hardware to accomplish this has been based on a PDP 11/20 minicomputer or a KIM microcomputer plus additional external hardware (13-15). The clock signal determines the rate at which the diodes are interrogated during readout and was 33 kHz with the minicomputer and 125 kHz with the microcomputer. This means the time to read out all 512 diodes and hence the minimum integration time varies from 15 ms to 3.7 ms, respectively. For the microcomputer, direct memory access (DMA) circuitry was used to increase the data acquisition rate. 

DMA - Direct memory access. A process where block of data can be transferred between main memory and secondary memory without processor intervention. 

In one-sided communication, one process controls the exchange of data with another process, and data exchange does not require cooperation of the sending and receiving processes. One-sided communication can be implemented via remote direct memory access, which enables a process to access (read from or write to) the memory of another process without explicit participation from the process whose memory is accessed. 

DMA Defense Mapping Agency direct memory access... 

DMA (direct memory access) controller Ethernet interface Memory controllers ... 

The I/O device becomes a controller that has direct memory access capability. As a result, it can place data in memory directly. 

The co-processor contains two independent 16-byte wide receive and transmit FIFO queues. Direct memory access (DMA) is supported to off-load the processor during reception and transmission. To receive data frames from the Ethernet line, the host CPU reserves a buffer space in main memory and invokes the co-processor. The asynchronously arriving data frames are received by the co-processor and stored into a local memory. A DMA receiver module then writes the data frames to main memory. To transmit data on the Ethernet line, the host CPU invokes the co-processor with a pointer to the location in main memory containing the data. The co-processor consmicts a data frame by reading the data fields from main memory and then transmits it over the Ethernet... 

Microprocessor 8085 has to be supported with some additional units to form the complete computer system. However, because of the request for direct memory access, more than minimum additional circuits were added. See Fig. 9.17 for the block diagram of the CPU board. The complete schematics of the CPU board are covered by 6 sheets ... 

Direct memory access controller central clock unit... 

After the direct memory access request, the normal... 

Direct memory access (DMA) is used to allow high speed data exchange between RAM and an external device. The operation of the system under the DMA conditions is shown in Fig. 9.20. The controller (see sheet 5 for schematics) provides three operating modes Read, Write and Read-Modify-Write (R-M-W). 

The controller can accept three direct memory access requests DCHRl, DCHR2, coming either from the Display Board or from Collecting Interface/Miscellaneous Boards. The third one, DCH3, might be used by the boards inserted into the option board slot. 

The display board also looks into the RAM using the direct memory access DMA to get the number of the stored counts in different channels. These data are combined with the information about the MCA working conditions which have to be displayed in text form in tne lower part of the screen. For this task, the display board is instructed which letter should be sent to MONITOR through the character video line CVID. 

Inside the CRT synchronizer unit, some additional control signals, like GTl, GT2 (dead time meter gate), CHEN (character gate), DGT (data gate), and SDMA (start direct memory access) are also derived. As inputs to A9, ROM IM 5610, signals from VERTICAL CELL COUNTER (AlO, All) are taken. 

Characters to be displayed are accepted from the local data bus (Fig. 9.32) during the direct memory access (DMA) cycle and loaded into the 8-bit character latch A91 (sheet 4) followed by another 8-bit latch. In this way a two-byte fast memory is... 

Direct Memory Access Logic and Address Generator... 

The direct memory access (DMA) is used to keep the CRT display refreshed and updated with real time data collection and text. This is done once per each Monitor vertical line, during the flyback. 

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