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HP 437B
Service Sheet BD1
The analog timer measures the width of the pulse at the output of the
analog-to-digital converter (in the Analog Section) and converts it to data
that can be interpreted by the microprocessor as a measurement.
The analog
timer also generates a microprocessor interrupt signal. This interrupt signal
occurs every 5 milliseconds.
The keyboard and display PIA provides the interface between the
microprocessor and the display/keyboard controller. Data from the data bus
is read by the PIA and sent to the display/keyboard controller.
Keystroke
information from the display/keyboard controller is read by the PIA. The
PIA places the data on the data bus where it is read by the microprocessor.
The display/keyboard controller is an 8-bit microprocessor.
The controller
detects keystroke information from the keyboard, converts it to parallel data
and transmits it to the microprocessor through the PIA. The microprocessor
sends display data through the PIA to the controller.
The controller then
sends the data to the display.
The service function switch consists of seven single-pole single-throw
switches.
These switches allow the user to set seven of the eight data lines on
the data bus to ground. Certain settings of these switches cause the
microprocessor to invoke certain self tests. The service function switch is
also used to set a default HP-IB address.
The LED data latch is used to convey operating information of the Power
Meter.
Data from the data bus causes the LEDs to illuminate or blink in
certain patterns.
These patterns convey information about errors and
operating states. More information about the LED data latch and service
function switch can be found in the troubleshooting information in this
section.
The HP-IB interface is a bi-directional device that allows the Power Meter to
interface with external instruments and controllers.
Control signals and data
from the data bus are received by the HP-IB interface and transmitted onto
the external HP-IB bus through two devices: the HP-IB transmit/receive
buffer and the HP-IB data control.
Similarly, control signals and data from
external instruments and controllers are received by the HP-IB interface and
transmitted onto the data bus.
Analog Section
The Analog Section measures the input signal from the power sensor.
The
signal is amplified, filtered, and then measured. The Analog Section then
produces a pulse with a width that is proportional to the power level of the
measured signal. This pulse width is counted by the Digital Section.
The
microprocessor converts this count to a power measurement.
Power levels (from an external source) are converted to a DC voltage.
A 220
Hz square wave signal from the power meter amplitude modulates the DC
voltage.
This creates a 220 Hz signal whose amplitude is proportional to the
sensed power level. The 220 Hz amplitude modulated signal from the power
sensor is fed into the input amplifier.
The input amplifier contains a shaping
network to compensate for non-linearities in ranges 4 and 5 of the power
sensor,
SERVICE
8-17
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