Fluke NetDAQ 2640A, Руководство по обслуживанию

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Theory of Operation
A1 Main to A3 A/D Converter Communications
2
2-45
Commands 2-79.
A command consists of a six-byte packet sent from the outguard to the inguard. The
most-significant four bits of the first bytes define the following command types:
•
Perform Scan.
•
Perform a Self-Test.
•
Return A/D Main Firmware Version.
•
Return A/D Boot Firmware Version.
•
Set Global Configuration.
•
Set Channel Configuration.
•
Do Houskeeping.
The sixth byte is a checksum. The meanings of the remainder of the bits in the command
packet vary depending on the command type. The response to all commands is one or
more six-byte response packets. The sixth byte in a packet is always the checksum byte;
the meaning of the remainder of the bits depends on the command. The only restriction
is that a response packet should always be distinguishable from a NAK, i.e., it should
never have all bits 1.
Perform Scan 2-80.
The Perform Command Packet tells the A/D Converter Assembly to do the following:
•
Measure Channel Number if set.
•
Return BR1 Zero Offset if set.
•
Return BR2 Zero Offset if set.
•
Return BR3 Zero Offset if set.
•
Return BR4 Zero Offset if set.
•
Return Reference Junction Reading if set.
•
Return Reference Balance (both references off) reading if set.
•
Return Reference Balance (both references on) reading if set.
•
Return Checksum.
Action Performed The Perform Scan command causes the inguard to measure each
channel indicated. These channels must have been previously defined using the Set
Channel Configuration command. One response packet is sent to the outguard for each
channel measured. If any thermocouple channels are requested in this scan, the first
response packet is the reference junction reading. If a requested channel has not been
defined, its value is returned as NaN.
There are several bits in the command that exist for debugging purposes only. These bits
indicate that the current stored value for the corresponding housekeeping reading should
be returned. The actual value returned for these bits depend on the current measurement
rate, since a different value is stored for each measurement rate. Note that these bits do
not cause any physical measurement to take place, they simply cause the latest values to
be returned.