Overrange Indications The digitizer indicates an overrange condition (input greater than the selected range can measure) by returning the values shown in Table 3-3.

An amplifier overrange (single-ended or differential input) sets bit 0 in the

Table 3-3. Digitizer Overload Readings

Condition

Reading

A/D Code

 

 

 

 

 

 

A/D Overrange

+9.900000E+037

+2047

(positive reading)

 

 

 

 

 

A/D Overrange

-9.900000E+037

-2046

(negative reading)

 

 

 

 

 

*S/E Input Amplifier

 

 

Overrange

 

 

or

-9.900000E+037

-2048

Differential Input

 

 

Amplifier Overrange

 

 

 

 

 

*A single-ended input amplifier overrange occurs when the input signal exceeds ± 5V.

A differential input amplifier overrange occurs on the 0.1V, 0.2V, 0.5V, 1V, 2V, and 5V ranges when the signal on the HI or LO input exceeds

±11V. An overrange occurs on the 10V, 20V, 50V, and 100V ranges when the signal on the HI or LO input exceeds ±110V.

digitizer’s Questionable Signal Status Register. However, the overrange does not generate an error message.

Retrieving Readings Each time the digitizer is INITiated it takes a new set of readings. Readings are retrieved directly from the A/D converters or from digitizer memory (Figure 3-11). Each new set of readings overwrites any readings currently in memory. Retrieved readings are transferred over the VME (VXI data transfer) bus or over the Local bus. The methods used to retrieve readings are listed below, relative to their transfer rates.

READ?

(page 139)

slowest

FETCh?

(page 139)

 

DIAGnostic:UPLoad:SADDress?

(page 141)

VME bus Data register access(page 146)

Local bus transfers

(page 156)

fastest

These methods are described in the following paragraphs. Table 3-4 summarizes the digitizer’s data transfer modes and transfer rates.

Chapter 3

Understanding the HP E1429 Digitizer 137

Page 137
Image 137
HP E1429A manual Read?