58 PCL-818L User's Manual
Direct memory access (DMA) improves system performance by
allowing external devices to transfer information directly to or from
the PC's memory without using the CPU. The PCL-818L's DMA
capability significantly improves the system performance in high
speed A/D applications.
Introduction to the 8237 DMA controller
The 8237 DMA controller chip on the PC system board handles the
DMA operation. This chip has four prioritized direct memory access
channels. Channel 0 is reserved by the PC system refresh its dynamic
RAM. Channel 2 supports floppy disk operations. Channel 3 is
normally used for hard disk operations. Channel 1 is not reserved for
any internal operations and is available for your applications.
Each channel has two associated control signals associated with it.
The DMA request signal (DRQ) triggers a DMA operation, and the
DMA acknowledge signal (DACK) authorizes the 8237 to start the
data transfer.
The 8237 DMA chip has four operating modes (single, demand, block
and cascade) and four control registers. These registers are:
1. Operation mode register (set mode of operation)
2. Address register (specify memory segment starting address)
3. Word count register (specify the number of transfers)
4. Initialization register (enable and disable DMA channels)
Note that you must properly set all four registers before requesting the
DMA operation.
Содержание PCL-818L
Страница 1: ...PCL 818L High performance DAS card with programmable gain ...
Страница 5: ...Chapter 1 General information 1 1 General information C H A P T E R ...
Страница 13: ...Chapter 2 Installation 9 C H A P T E R 2 Installation ...
Страница 25: ...Chapter 3 Signal connections 21 3 Signal connections C H A P T E R ...
Страница 31: ...Chapter 4 Register structure and format 27 4 Register structure and format C H A P T E R ...
Страница 41: ...Chapter 5 A D conversion 37 C H A P T E R 5 A D conversion ...
Страница 47: ...Chapter 6 D A conversion 43 6 D A conversion C H A P T E R ...
Страница 50: ...46 PCL 818L User s Manual ...
Страница 51: ...Chapter 7 Digital input and output 47 7 Digital input and output C H A P T E R ...
Страница 53: ...Chapter 8 Programmable counter timer 49 8 Programmable timer counter C H A P T E R ...
Страница 61: ...Chapter 9 Direct memory access operation 57 9 Direct memory access operation C H A P T E R ...
Страница 64: ...60 PCL 818L User s Manual ...
Страница 65: ......
Страница 66: ...Appendix B Connector Switch and VR Locations 63 B Connector switch and VR Locations A P P E N D I X ...
Страница 68: ...Appendix C PC I O port address map 65 C PC I O port address map A P P E N D I X ...
Страница 70: ...Appendix D Calibration 67 D Calibration A P P E N D I X ...
Страница 73: ...70 PCL 818L User s Manual ...
Страница 75: ...2 PCL 818L User s Manual ...