Chapter 5: analog inputs, 1 introduction, Analog inputs – Sensoray 826 User Manual
Page 18: Introduction
Chapter 5: Analog Inputs
5.1 Introduction
The board's analog input system consists of the following major elements:
•
Analog multiplexer (Mux) - selects one of 16 differential input pairs (channels) for conversion.
•
Programmable gain amplifier (PGA) - applies voltage gain of 1, 2, 5, or 10 to the selected input.
•
Analog-to-digital converter (ADC) - performs an analog-to-digital conversion in three microseconds or less.
•
Controller - manages operation of the analog input system.
Figure 3: Analog input system
Analog-to-digital (A/D) conversions are performed in bursts of up to 16 conversions. Each conversion takes place in a
timeslot (called a slot), which is a reserved time interval within a burst. During a burst, slots are processed in numerical
order beginning with slot 0 and ending with slot 15.
Every slot has three attributes that are programmed into its slot configuration register via the S826_AdcSlotConfigWrite
function:
•
Analog channel number: designates the analog input channel that will be digitized when the slot is processed. Any of
the 16 channels may be assigned to any slot. A channel may be assigned to two or more slots if desired.
•
PGA gain: specifies the analog gain to apply to the analog input signal.
•
Settling time: specifies the delay from analog multiplexer switching to start of digitization.
The slotlist register designates each slot as either active or inactive; this is programmed via the S826_AdcSlotlistWrite
function. When a burst occurs, each slot is processed according to the slotlist. An active slot is processed by performing one
A/D conversion; its total time is the sum of its settling time plus a fixed conversion time. Inactive slots are skipped and
consume no time during a burst (the slot configuration register is ignored for an inactive slot). The total processing time of
each slot is configurable, from zero (inactive slot) to approximately 335 milliseconds, in one-microsecond increments.
826 Instruction Manual
13
Analog Inputs
Result
Registers
Slot Config
Registers
Trig Mode
Register
Slotlist
Register
M
ux
PGA
DIO_in signals
ADC
BurstNum
Timestamp
16 Differential
Input Pairs
Overrun
Internal
Data Bus
Interrupt System
IRQ
Trig
6
48
CTR_out signals
Controller
32
8
16
6
Virtual output signals
Hold
Registers