ADLINK ACL-8112 Series - Manual (Page 52)

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• Operation Theory
5.1.3 A/D Data Transfer Modes
On the ACL-8112, there are three A/D data transfer modes that can be used
when A/D conversion is completed. The data transfer mode is controlled by
the mode control register (BASE+11). The different transfer modes are
described below:
Software Data Transfer
Usually, this mode is used with software A/D trigger mode. After the A/D
conversion is triggered by the software, the software will poll the DRDY bit
until it becomes high. Whenever the low byte of the A/D data is read, the
DRDY bit will be cleared to indicate the data has been read.
It is possible to read the A/D converted data without polling. The A/D
conversion time will not excess 8
µ
s on the ACL-8112 card. Hence, after a
software trigger, the software can wait for at least 8
µ
s then read the A/D
register without polling.
Interrupt Transfer
The ACL-8112 provides hardware interrupt capability. Under this mode, an
interrupt signal is generated when an A/D conversion has ended and the data
is ready to be read. It is useful to combine the interrupt transfer mode with
the timer pacer trigger mode. Under this combination, the data transfer is
essentially asynchronous with the controlling software.
When the interrupt transfer mode is used, you have to set the interrupt IRQ
level using hardware jumpers. Refer to section 2.10 for IRQ jumper setting.
After an A/D conversion is completed, a hardware interrupt will be inserted
and its corres ponding ISR (Interrupt Service Routine) will be invoked and
executed. The converted data is transferred by the ISR program.
DMA Transfer
The DMA (Direct Memory Access) allows data to be transferred directly
between the ACL-8112 and the PC memory at the fastest possible rate,
without using any CPU time. The A/D data is automatically transferred to
PC's memory after conversion is completed.
The DMA transfer mode is very complex to program. It is recommended that
a high level programming library be used to operate this card in this mode. If
you wish to program a software which can handle DMA data transfer, refer to
information about the 8237 DMA controller.