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The current-channel value is incremented only when the ADC is sampled or triggered. For every ADC trigger, the
current-channel is incremented. The current-channel is presented as CH[3:0] in the ADC Status Register ( see page 60).
If the STX104 is configured for differential input mode, the most significant bit of the current-channel (and therefore first- and
last-channel) is ignored.
If the FIFO function is enabled, the user software must track the channel being read out of the FIFO. In other words, it is the
software which must maintain synchronization.
If the first-channel is the same as the last-channel, then the analog channel (multiplexer) is not changed. This can be useful for
sampling the same channel continuously.
It is recommended to have first-channel < last-channel to prevent confusion of the channel sequencing as illustrated in examples
(C) and (D) below.
FIFO RESET
Writing to the channel register will reset the FIFO when the FIFO Superset mode is enabled (jumper M1 is installed) and/or
DAS1602 mode enabled (jumper M0 is installed).
ACQUISITION CONTROLLER RESET
Writing to the Channel Register resets the internal acquisition controller in all modes.
MOVING AVERAGE FILTER RESET
Writing to the Channel Register also resets the internal moving average filter in all modes when jumper M3 is installed. The CNV
bit (see ADC Status Register ( see page 60)) will become active for approximately six microseconds while the moving average
filter is reset.
SS&H OUTPUT
The Start Sample and Hold (SS&H) signal, at pin 14 of the I/O connector, is a TTL output used to drive the sample and holds line
of external simultaneous sample and hold cards. The behavior of the SS&H output signal is related to the Channel Register.
Writing any value to the Channel Register will bring the SS&H line active high. The SS&H line will go low, indicating a hold, when
the first_channel sampling has completed (i.e. the input multiplexers now looking at the next channel). The SS&H line will return
high when last_channel has been sampled and the multiplexers wrap back to the first_channel.
See Also
Register Summary ( see page 41)
11.6 ADC Channel (Offset=2)
STX104 Reference Manual
Copyright © 2009 by
Apex Embedded Systems
. All rights reserved.
Thursday, October 08, 2009
51
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