Xycom XVME-500, Manual

Page: 56 / 104

XVME-500/590 Manual
February, 1988
When reading the A/D input data, however, the high byte (base + 86H) must be read
before the low byte (base + 87H); or they must be read simultaneously.
This
stipulation is mandatory because a read from the low data byte will initiate a new
A/D conversion if the module is operating in either the sequential or single-
channel conversion mode.
Thus, it would write over the information contained in
the higher byte.
Figure 3-5 shows the format of the A/D data input register.
High Byte Low Byte
D15 D14 D13 D12 Dll
Dl0
D9 D8 D7
D6 D5 D4 D3
D2 Dl D O
Base + 86H Base + 87H
Figure 3-5. A/D Data Input Register Format
The manner in which data appears at the A/D Data Register depends upon which
input operation mode has been previously programmed (see Section 3.3.1.1 for the
explanation of status/control bits D5 & D6; and Section 3.4 for information on the
analog input modes).
3.3.4.1
A/D Data Format
The A/D converter digitizes the value of an analog signal on the input of a selected
channel. The digital format of the converted data depends upon which data format
and input voltage mode (unipolar or bipolar) have been previously jumpered at
module installation (see Sections 2.6.1 and 2.6.2).
3-11
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