Measurement Computing DAQFlex - Manual (Page 44)

DAQFlex Message-based Firmware Specification Hardware Reference – USB-7204
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o When set to ENABLE/GSLAVE, the first clock pulse after setting up the scan is held off to ensure
adequate setup time for the first conversion. No pulses are ignored. Use this mode when the
device is paced from another USB-7204.
 1024 bytes of nonvolatile EEPROM memory; used for storing configuration information, calibration
data, and user data.
 RATE takes a float value.
If the input scan rate requested is less than the slowest rate supported by the device, the device is
set to the slowest rate supported by the device. If the input scan rate requested is greater than the
fastest rate supported by the device, the device is set to the maximum rate supported by the
device.
 Bulk transfers
o Bulk transfers from endpoint 1 IN are used for analog input scans. Data is in RAW format and
"DEV:DATATYPE" has no impact on the data.
o Bulk transfers to endpoint 2 OUT are used for analog output scans. Data is transmitted in two
bytes per channel, with the 12-bit representation packed into the lower 16-bits and transmitted
in RAW format, resulting in an output of 0-4.096 V.
The device is preloaded with up to 1024 bytes. The device will ACK while it is filling. When the
four internal 256-byte buffers are filled, the device will NAK until an analog output scan is
started.
If a data underrun occurs, the device stalls the BULK OUT endpoint (EP_2) when the AOSCAN
STALL property is set to ENABLE. To clear the stall, send AOSCAN:RESET or start a new scan.
The STALL property is disabled by default.
o The bulk transfer size must be a multiple of the USB maximum bulk packet size.
Analog input data format
Note: This section applies to data acquired using firmware versions ≥2.03. For data acquired using
firmware versions ≤2.02, refer to the data format shown below in Table 3 .
When performing analog input operations with the "AI" component, the return data is LSB (Least
Significant Bit) justified with a value of 0 as Min Scale.
When performing analog input operations with the "AISCAN" component, the differential return data is
12-bit MSB (Most Significant Bit) justified. Additional steps are required to convert single-ended data to
11- or 12-bit representation (LSB justified).
The bit tables below show the data for each operating mode, and lists the steps to convert the data to
LSB justified.
Differential mode
Table 1 applies to data acquired using firmware ≥2.03.
Table 1. A/D Converter Values (differential mode)
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Data x x x x x x x x x x x x 0 0 0 OVR
where:
x The actual conversion value.
OVR 0 = Valid conversion
1 = An analog over-range problem has occurred in the PGA; the conversion value may be
invalid. Note: this bit can be ignored.