Analog Input
VSBC-8 Reference Manual
Reference
–
35
A
NALOG
C
ONTROL
R
EGISTER
ACR (WRITE) 00E4h (or 1E4h via CMOS Setup)
D7
D6
D5
D4
D3
D2
D1
D0
PD1
PD0
ACQMOD
RNG
BIP
A2
A1
A0
Table 17: Analog Control Register Bit Assignments
Bit
Mnemonic
Description
D7, D6
PD1, PD0
Clock and Power-Down Selection
— These bits select the power savings
mode and clock source for the A/D circuit.
PD1
PD0
Mode
0
0
Normal Operation / External Clock Mode
0
1
Normal Operation / Internal Clock Mode
1
0
Standby Power-Down (STBYPD)
1
1
Full Power-Down (FULLPD)
Note!
STBYPD and FULLPD selections do not affect the clock mode.
D5
ACQMOD
Acquisition Mode
— This bit selects the type of acquisition mode.
ACQMOD = 0
Internal Acquisition. A write to the ACR register will initiate
an acquisition interval whose duration is internally timed. Conversion starts
when this six-clock-cycle acquisition interval (3.26µs) ends.
ACQMOD = 1
External Acquisition. Use this mode for precise control of the
sampling aperture and/or independent control of acquisition and conversion
times. The acquisition and start-of-conversion is controlled with two separate
writes to the ACR register. The first write, written with ACQMOD = 1, starts
and acquisition interval of indeterminate length. The second write, written with
ACQMOD = 0, terminates acquisition and starts conversion. However, if the
second write contains ACQMOD = 1, an indefinite acquisition interval is
restarted.
Note!
The address bits for the input mux (A0–A2) must have the same values on the
first and second write pulses. Power-down mode bits (PD0, PD1) can assume new
values on the second write.
D4, D3
RNG, BIP
Range and Polarity Selection
— These bits select the input range and
polarity on a channel-by-channel basis.
RNG
BIP
Input Range
0
0
0 to +5V
1
0
0 to +10V
0
1
±5V
1
1
±10V
Warning!
The board can be damaged if voltages in excess of ±16V are applied
.
D2-D0
A2, A1, A0
Input Channel Address
— These bits select which input channel you wish to
convert.
A2
A1
A0
Channel
0
0
0
Channel 0
0
0
1
Channel 1
0
1
0
Channel 2
0
1
1
Channel 3
1
0
0
Channel 4
1
0
1
Channel 5
1
1
0
Channel 6
1
1
1
Channel 7
