500-003111-000
4-9
Method
One
a. Increasing the Gain:
First, select the Channel, then select the increased Gain.
b. Decreasing the Gain:
First, select the lower Gain, then select the Channel.
Method
Two
When changing the Gain:
First, select the Gain of x1; second, select the channel; then third, select
the required Gain.
4.6 CONTROLLING
AND READING THE ADC
Two principal methods are available for controlling the ADC on the
VMIVME-3111 board. For applications in which conversion speed is not a critical
factor, the basic method usually will provide suitable performance. This is the
simpler of the two methods to implement and will produce a maximum throughput on
the order of 35 kHz (35,000 samples per second).
If higher throughput is essential, the interleaved (pipelined) method can be
used. The interleaved control approach permits the settling interval of a new channel
to begin while a conversion is in progress. This technique eliminates the settling
interval from the throughput equation (Section 3), and raises the throughput to
approximately 59 kHz.
4.6.1 ADC
Timing
All basic timing operations for the ADC are performed by the on-board
controller. Control of the converter consists of the "handshake" programming
sequences described in the following paragraphs.
4.6.2
ADC Controls and Flags
The following controls, flags, and registers are available for use in
controlling the ADC (controls and flags are summarized in Tables 4.2-1 and 4.2-2).
CONTROLS (CONTROL REGISTER)
a. START SETTLING H ..................D06
b.
TWO'S
COMPL L.........................D12
c.
EN
START
CONV H ...................D13
FLAGS (STATUS REGISTER)
a.
SETTLING
BUSY H ....................D06
b.
CONV
BUSY H ............................D13
c. NEW DATA RDY H ......................D15 (Set when data is available in
the A/D Data Register)
*Effective only upon writings (i.e., "strobed").
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