Table of Contents
Advertisement
4-54
The second highest priority interrupt is not shown on
the block diagram, and is used only for manufacturing test at
the factory.
4455
The POWER MESH STATUS lines (Ml, CC, M2, CV,
OT,
QV)
drive
the
third
level
interrupt.
Once
the
microprocessor has noted a power mesh interrupt, the
microprocessor monitors the power mesh continuously via
CRUIN. The microprocessor then disables the POWER MESH
INTERRUPT ENABLE so that low priority interrupts can
operate. Note that the POWER MESH STATUS signals only
interrupt the microprocessor via this circuit, they do not tell
the microprocessor the power mesh status. The POWER
MESH STATUS signals are sent to the I/O inputs circuit on
the front panel, where they are loaded into the microprocessor
via CRUIN once the microprocessor responds to the interrupt.
4-56
HP-IB INTERRUPT is the fourth level microprocessor
interrupt. As explained in the HP-IB Circuit section, the
microprocessor has to load a status byte in via CRUIN to
determine the exact cause of an HP-IB INTERRUPT.
4-57
The lowest priority microprocessor interrupt is the 1
MILLISECOND
TIMER
signal,
which
comes from the
microcomputer bias power supply circuit. This signal is used
by the microprocessor to time the service-request delay after
new output values have been programmed. The interrupt also
causes the microprocessor to load CRUIN so it can check the
Rotary Pulse Generator Decoders to determine if the front-
panel OUTPUT ADJUST control has been turned and check if
the OUTPUT ADJUST pushbutton is pressed.
4-58
Microprocessor interrupts are encoded onto three
lines, ICO, iCI, and IC2, which connect to the microprocessor.
This three-line code represents the highest level interrupt
recognized by the microprocessor interrupts circuit.
Generator
4-64
The three DAC circuits, one each to control output
voltage, output current, and OVP trip voltage, are similar.
Address lines address each latch in turn, eight for OVP and
twelve each for voltage and current, and data from CRUOUT
is loaded. The analog outputs from the DACs are connected
to front-panel reference circuits, whose outputs are compared
to the actual power supply output.
4-05
FRONT-PANEL ASSEMBLY
4-66
Figure 4-4 is a block diagram of the front-pane!
assembly, which contains the microprocessor I/O circuits,
output current, voltage and OVP reference circuits, the rotary-
pulse generator, and the front-panel display circuits.
4-67
I/O Inputs
4-68
This circuit multiplexes data concerning the status of
the power mesh, the OUTPUT ADJUST controls, and the CV
and CC readback comparators onto the microprocessor
CRUIN line. Note that CRUIN will be loaded at least once
every millisecond because of the interrupt generated by the
1ms timer, so even very rapid operation of the OUTPUT
ADJUST controls will be observed.
/O Ouptuts
4-70
The microprocessor CRUOUT is connected to ad¬
dressable latches in this circuit. Sixteen of these latches drive
the LEDs on the front panel. Other outputs tell the
Microprocessor Interrupts circuit which operating mode is
selected so that circuit can compare the actual operating
mode (CV or CC) to the selected mode (Ml or M2). The
microprocessor also uses CRUOUT to reset the Rotary Pulse
Generator Decoders and OVP, enable or disable power mesh
interrupts, and request service.
4 00
Clock pulses are required to shift data from the Data
Shifters across isolation to the microprocessor CRUIN. The
CRU
Clock
Generator
monitors
which
address
the
microprocessor is looking at. When the circuit notes that the
microprocessor has advanced to the next address, a clock
pulse is generated. Other inputs to this circuit determine
whether the pulse is connected to T2, T3, or both.
4-62
This
circuit
decodes
which
address
the
microprocessor is addressing and enables various gates in the
microcomputer circuits and on the front-panel assembly to
determine where data will be sent to or received from. For ex¬
ample, the outputs from this circuit determine whether CRU
Clock pulses are connected to T2 or T3. Other outputs deter¬
mine which DAC is loaded, and which I/O latches are enabled.
4-71
Constant Current Reference Circuit
4-72
The CC reference circuit receives the CC DAC output
signal and produces from it the 0-volt to 5 volt CC program¬
ming voltage that is supplied to the CC control circuit on the
control board.
4 73
Figure 4-5 is a simplified schematic of the CV and CC
reference circuits, showing the relationship of components on
the HP-IB/microcomputer assembly and the front-panel
assembly. Reference designators in parenthesis are for CC cir ¬
cuit components, others are for CV circuit components.
4-74
As can be seen, the analog output from the DAC is
applied to a reference amplifier circuit. The feedback resistors
for the reference amplifier are in the DAC package, so that any
temperature-induced drift is self correcting. The reference
Advertisement
Table of Contents
