18
3.3.1 Figure 3-43.3.1 Local Mode
In the local mode, control signals are generated either by the microprocessor or directly from
the front panel, depending on the signal. Frequency, power factor, deviation and Operate/Standby
signals are derived from individual front panel controls and coupled to logic through remote/local
multiplexers. Voltage, volt-amperes, current and VA/seconds or KVA/seconds are entered via the
keyboard into the microprocessor and then to storage registers. The parameters entered via the front
panel either directly or through the microprocessor are combined in the logic circuits to make signals
suitable for use in controlling the voltage, current and power factor function.
3.3.2 Directly Applied Control Signals
The direct signals are multiplexed on the Control Logic Assembly (08-113-001/2):
The frequency selection signal goes directly to MPXR IC25 and then to frequency selecting
switches on the Oscillator IC2, 3, 4 and 5. The 60Hz signal also goes to the Phase Control and
Sense to select the integrator time constant. The oscillator vernier control goes to the Oscillator to
assert U13-16.
The power factor BCD values go directly to the Phase Control and Sense where the 10's
compliment is formed in IC5 and applied to U8-U11 to synthesize the value 10 (1-COS 0) volts. The
lead/lag signals are used likewise to operate U6 and U7. The power factor BCD values go also to the
reference to inhibit the deviation function at "0" power factor, and to scale the deviation for other
values via U3 through U6.
The deviation range selection goes to the Reference and selects the 0.1% or 1.0% range via
U1 and U2, and turns on the error display meter through Q6.
The Operate and Standby signals are used in the Control Logic respectively at IC15-5 and
IC14-10 and logically coupled to the one shot multi-vibrators of IC19. The outputs of IC19 set or
reset flip flops which in turn activate the Standby/Operate relays K6, K6A and K8 and the Operate
and Standby LED displays.
3.3.3 µP Treated Signals
The microprocessor circuits are shown in detail on schematic 08-125-001. The circuits
consist of the microprocessor (µP) IC26, the fixed memory, IC25, the input/output multiplexer or PIA,
IC18 and output storage registers IC8-1 5 and IC36-42. If the remote IEEE 488 option is used the
IEEE 488 bus lines are accessed through the 488 chip, IC7. All other integrated circuits perform
functions to support these main components.
On power up the µP performs a series of self checks. These include a ROM check, a RAM
check and an in initialization check. Also the ROM revision number is output to the voltage field, the
IEEE address code is output to the current field and the option code is output to the VA field on the
front panel. If the self check sequence is failed the status byte, available over the IEEE-488 interface,
will be all ones, a value of 255 and in all cases no information will be output to the various fields.
The µP initializes at power up or reset, sets the output registers to a preassigned null
condition and places itself in the monitor loop, waiting for the entry of a voltage setting through the
keyboard. The keyboard is connected via J23 to IC10 which decodes the keyboard entry and applies
it directly on data lines of the µP, IC26, as input data.
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