User`s guide

Operation Theory • 37
Timebase clock source
In scan acquisition mode, all the A/D conversions start on the output of
counters, which use Timebase as the clock source. With the software you can
specify the Timebase to be either an internal clock source (on board 24MHz) or
an external clock input on pin 45 of J1. The external clock is useful when you
want to acquire data at rates not available with the internal A/D sample clock.
The external clock source must generate TTL-compatible continuous clocks,
and the maximum frequency is 24MHz while the minimum is 1MHz.
Acquisition_in_progress
Scan_start
AD_conversion
Scan_in_progress
(
SSH_OUT
)(pin47)
3 Scans, 4 Samples per scan
(SC_Counter=3, DIV_Counter=4)
Sampling Interval t=
SI2_COUNTER/TimeBase
Scan Interval T=
SI_COUNTER/TimeBase
Ch2
Ch3
Ch1
Ch0
Ch2
Ch3
Ch1
Ch0
Ch2
Ch3
Ch1
Ch0
( channel sequences are specified in Channel Gain Queue)
Figure 9: Scan Timing
In the scan acquisition mode, the channel, gain, and input configurations
(single-end, differential, or U_CMMD) must be specified in the hardware
Channel Gain Queue, please refer to 5.1.3.2 for more details.
There are 5 trigger modes to start the scan acquisition, please refer to 5.1.3.3
details. The data transfer modes will be discussed in 5.1.3.4.