19
After the voltage is entered, the µP awaits the entry of VA data and for the Model 811A
VA/seconds, KVA/seconds or events data.
As each digit is stroked on the keyboard and entered, it is processed and appears in the
output registers and display. For example the first voltage digit stroked appears at the output register
IC38; the next stroke moves the first digit entered to the V10 position in IC39, etc. until all three digits
are entered and appear as outputs in the V1, V10 and V100 positions. Simultaneously the register
outputs are displayed.
After the VA data is entered and stored in output registers as W1-W10K, the µP computes
the current I = VA/V and stores it in the output registers as I1-I1 0K. For the Model 811A, after the VA
data is entered, the VA/second, KVA/second or events data is entered and stored as WS1-WS10K.
Both current and VA -seconds or events are displayed.
Built into the µP module is an auto repeat feature which is initiated when holding a key
depressed. This is useful when entering many identical numbers.
3.3.4 Use of µProcessor Generated Control Signals
The BCD voltage data V1, V10 and V100 is directed to the Control Logic, where the digit data
is shifted depending upon range, ultimately applying it to IC4, a digital to analog converter on the
CVA. The other voltage related signal 121 -/<V-/< 280 is used in the Control Logic.
The Current BCD data I-I10K is directed to the CVA where it controls the current D to A
converter. The current range data IDP XXX is used in the Control Logic to activate the selection of
current shunts on the Output Board. The current range information is also used to generate via IC20
of the Control Logic a momentary shutdown when ranges are changed. This allows shifting of ranges
without the need to enter and enable Standby/Operate.
The VA/second data is used to generate the VA/second gate (i.e. the time taken at the set
value of VA to produce the set value of VA/seconds) at IC21 pin 12 of the µP module.
Other less significant control functions may be found by detailed examination of the control
logic schematic.
3.3.5 Remote Mode
In the remote mode all data is entered and extracted in serial ASCII characters through the
IEEE 488 Interface on J7. IC3-6 are bus transceivers under control of IC7 pin 27. Operation is
identical to that described previously except that frequency, deviation range and power factor are now
µP derived signals appearing at IC8 and 9 of the µP assembly. Also the reading of the % error Meter
is applied to the µP data lines through J44 and the PIA IC18 of the µP assembly. This data is then
transmitted to the IEEE Bus when requested. Further description of the IEEE 488 Interface, including
the syntax, is provided in Section 5.
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