CHAPTER 5
ADVANCED PROGRAMM1N TECBNIQUES
51
5. ADVANCED PROGRAMM1N TECBNIQUES
5.1. Direct Memory AcceAs (DMA)
Direct memory acaess (DHA) improves system performance by allow- ~ ing external
devices to directly transfer information to or from 3 the system memory without
operation of the system CPU. Any I/O ~ port can source data for DMA and any
read-write memory location ~¤ can receive data. The IEEE-488 interface data transfer
can be programmed to proceed with or without DMA. When you use DMA, the
IEEE-488 interface card provides a number of unique and powerful features.
These features include :
1) The ability to run application programs and DMA simultaneously. It means the
data transfer between PC and the IEEE-488 bus can be background operated.
2) Selection of two DMA operating modes : single byte transfer mode or block
transfer mode.
3) The ability to run IEEE-488 DMA and disk DMA simultaneously.
4) The ability to continuously transmit or receive data blocks of up to 64K bytes
without processor overhead.
These features can significantly improve system performance in applications where
high speed transfers are required or large blocks of data must be moved.
This section describes how DMA works and how you can use it to your advantage. It
also introduces and explains Bit 15 and 14 of <SETTING%> of the INIT routine
described in Section 3.3.7.
DMA is controlled by the 8237 DMA controller chip on the PC’s system board. It
performs dynamic RAM refresh, and supports data transfer between floppy disks
and hard disks in addition to serving the IEEE-488 interface.
Like all DMA chips, the 8237 DMA chip is designed to perform one basic function.
That function is to transfer data between memory and I/O devices. It performs the
transfer by simultaneously addressing the memory location and I/O device and
providing the appropriate read and write signals.
The 8237 DMA chip has four DMA channels, four operating modes, and four
operating conditions. Each channel has a mode register that determines the four
operation conditions of the DMA channel.
These conditions are:
1) The direction of transfer (input or output).
Содержание PCL-848A/B
Страница 1: ...PCL 848A B MULTIFUNCTION IEEE 488 INTERFACE CARD ...
Страница 5: ...10 ASCII TABLE 74 11 NEC7210 RBAD WRITE REGISTSR 76 12 SUMMARY OF TBE IEEE 488 LIBRARY FUNCTIONS 77 ...
Страница 6: ...Figures Fig 2 2 Location of switches and jumpers 4 Fig 7 1 PCL 848A B Block Diagram 59 ...
Страница 65: ...CHAPTER 7 TBEORY OP OPERATION 59 Fig 7 1 PCL 848A B Block Diagram ...
Страница 76: ...70 PCL 848AB User s Manual ...
Страница 78: ...72 PCL 848AB User s Manual Handshake Timing Sequence ...
