SD16_A Operation
28-6
SD16_A
28.2.5 Analog Input Pair Selection
The SD16_A can convert up to 8 differential input pairs multiplexed into the
PGA. Up to five analog input pairs (A0-A4) are available externally on the
device. A resistive divider to measure the supply voltage is available using the
A5 multiplexer input. An internal temperature sensor is available using the A6
multiplexer input. Input A7 is a shorted connection between the + and − input
pair and can be used to calibrate the offset of the SD16_A input stage.
Analog Input Setup
The analog input of each channel is configured using the SD16INCTLx
register. These settings can be independently configured for each SD16_A
channel.
The SD16INCHx bits select one of eight differential input pairs of the analog
multiplexer. The gain for each PGA is selected by the SD16GAINx bits. A total
of six gain settings are available.
On some devices SD16AEx bits are available to enable or disable the analog
input pin. Setting any SD16AEx bit disables the multiplexed digital circuitry for
the associated pin. See the device-specific data sheet for pin diagrams.
During conversion any modification to the SD16INCHx and SD16GAINx bits
will become effective with the next decimation step of the digital filter. After
these bits are modified, the next three conversions may be invalid due to the
settling time of the digital filter. This can be handled automatically with the
SD16INTDLYx bits. When SD16INTDLY = 00h, conversion interrupt requests
will not begin until the 4
th
conversion after a start condition.
On devices implementing the high impedance input buffer it can be enabled
using the SD16BUFx bits. The speed settings are selected based on the
SD16_A modulator frequency as shown in Table 28−1.
Table 28−1.High Input Impedance Buffer
SD16BUFx
Buffer
SD16 Modulator Frequency f
M
00
Buffer disabled
01
Low speed/current
f
M
< 200 kHz
10
Medium speed/current
200 kHz <
f
M
< 700 kHz
11
High speed/current
700 kHz <
f
M
< 1.1 MHz
An external RC anti-aliasing filter is recommended for the SD16_A to prevent
aliasing of the input signal. The cutoff frequency should be < 10 kHz for a
1-Mhz modulator clock and OSR = 256. The cutoff frequency may set to a
lower frequency for applications that have lower bandwidth requirements.
Summary of Contents for MSP430x4xx Family
Page 1: ...MSP430x4xx Family 2007 Mixed Signal Products User s Guide SLAU056G ...
Page 2: ......
Page 6: ...vi ...
Page 114: ...3 76 RISC 16 Bit CPU ...
Page 304: ...5 20 FLL Clock Module ...
Page 340: ...7 8 Supply Voltage Supervisor ...
Page 348: ...8 8 16 Bit Hardware Multiplier ...
Page 372: ...9 24 32 Bit Hardware Multiplier ...
Page 400: ...10 28 DMA Controller ...
Page 428: ...13 10 Basic Timer1 ...
Page 466: ...15 24 Timer_A ...
Page 522: ...17 30 USART Peripheral Interface UART Mode ...
Page 544: ...18 22 USART Peripheral Interface SPI Mode ...
Page 672: ...23 12 Comparator_A ...
Page 692: ...24 20 LCD Controller ...
Page 746: ...26 28 ADC12 ...