Chapter 5
Theory of Operation and Register-Level Programming
©
National Instruments Corporation
5-3
The DIP switch attached to the scanning counter configures the
AMUX-64T for one-board, two-board, or four-board operation. Individual
AMUX-64T boards are selected depending on the higher-order two bits of
the scanning counter.
The AMUX-64T contains an onboard switch to either power the
AMUX-64T from the MIO board or to 5 V externally. From the
+5 V power, an onboard DC-to-DC converter generates a ±15 V source,
which is used to power the multiplexers. The MIO board can supply enough
+5 V power to drive up to four AMUX-64T boards except the MC-MIO-16,
which can power only two boards.
How to Address AMUX-64T Analog Input Channels
A/D Conversions on a Single AMUX-64T Analog Input Channel
Before an AMUX-64T channel can be selected, digital I/O port A must be
enabled as a digital output port. You can enable this port by setting the
DOUTEN0 bit in the MIO Command Register 2 (this bit has different
names depending on your MIO board). This bit needs to be set only once
after initializing the MIO board.
The scanning counter is used to select individual multiplexer inputs and
individual AMUX-64T boards. The bit assignment for the scanning counter
and MIO board digital I/O port A is shown in Figure 5-2.
Figure 5-2.
Scanning Counter Control Bits
Bits ADO0 and ADO1 address each four-to-one multiplexer on the
AMUX-64T and work in combination with the MIO Mux-Gain Register
(the Mux-Mem Register in the AT-MIO-16F-5) to select the analog input
channel. An address map for selecting analog input channels on a single
AMUX-64T is shown in Table 5-1.
ADO3
ADO2
ADO1
ADO0
These Digital Output Register bits are
loaded into the Scanning Counter and
used to select AMUX-64T channels
Channel Select
Board Select
3
2
1
0
