PCIe-24DSI32
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General Standards Corporation Ph:(256)880-8787 FAX:(256)880-8788 Email: [email protected]
3-17
3.7 Autocalibration
Autocalibration is an embedded utility that calibrates all input channels to a single internal
voltage reference. Offset and gain error corrections for each channel are determined during
autocalibration, and are applied to each channel in real-time during data acquisition. The
correction values are retained until either: (a) power is removed, (b) a PCI reset occurs, or
(c) autocalibration is invoked again. Autocalibration is invoked by setting the AUTOCAL control
bit HIGH in the BCR. Completion of autocalibration is indicated by the AUTOCAL flag clearing
automatically to the LOW state. Clearing of the AUTOCAL control bit is selectable as an
interrupt request event.
An autocalibration sequence has a typical duration from 5 to 11 seconds*, depending upon the
selected sample rate and the number of active channels. Read or write access from the PCI
bus during autocalibration may disrupt the calibration process, and should be avoided. Either a
suitable delay or the "Autocal Completed" interrupt should be used to detect the end of
autocalibration.
* NOTE: Early firmware revisions may exhibit shorter autocaibration durations.
If a board is defective, the autocalibration process may be unable to successfully calibrate all
input channels. If this situation occurs, the AUTOCAL PASS status flag in the BCR will be
LOW when the autocal sequence is completed. A HIGH state for AUTOCAL PASS indicates
that autocalibration was successful.
To ensure full conformance to the product specification, autocalibration should always be
invoked after:
(a). Power has been applied to the board,
(b). A PCI reset event has occurred,
(b). The input range, clock source or sampling rate has been altered,
(c). A scan-synchronization sequence has been performed (Section 3.10.
Autocalibration can be invoked at any time, but should not occur while the system is
experiencing a major environmental transition such as that which usually occurs directly after
power is applied. For optimum performance, a warmup delay of 15 minutes is recommended.
3.8 Interrupt Control
In order for the board to generate a PCIe interrupt,
both
of the following conditions must occur:
a. The internal controller must generate a Local Interrupt Request
b. The
PCIe interrupt
must be enabled.
If the internal controller generates a local interrupt request, a PCIe bus interrupt will not occur
unless the PCIe interrupt has been enabled as described below in Paragraph 3.8.2.
3.8.1 Local Interrupt Request
The single local interrupt request line is controlled by the INTERRUPT A[2:0] and INTERRUPT
REQUEST FLAG control bits in the BCR. The condition for the interrupt request is selected as
shown in Table 3.8.1. When the selected condition occurs, a local interrupt request is
generated and the INTERRUPT REQUEST FLAG bit is set in the BCR. The request remains
asserted until the PCIe bus clears the BCR request flag. A local interrupt request is generated
automatically at the end of initialization.
