Chapter 6 339
General Troubleshooting
Block Diagram Description
trigger signal is received from a rear panel BNC connector. A DAC in
the trigger circuit sets the video trigger level. The trigger circuit is
responsible for setting HSCAN high.
Controller Section
The controller section includes the A2 controller assembly and A19
HP-IB assembly. The battery on the rear panel provides battery backup
for state and trace storage.
In 8560EC instruments the A2 contains the CPU, RAM, ROM, the
display ASM, Fast ADC circuitry, HP-IB interface, control, frequency
counter, display RAM, option module interface, and EEROM.
In 8560E instruments the A2 contains the CPU, RAM, ROM, the
display ASM and line generators, CRT blanking, focus, intensity, HP-IB
interface, control, frequency counter, display RAM, option module
interface, and EEROM. In 8560E instruments the A2 assembly controls
the A17 CRT driver through W7.
The A19 HP-IB is a mechanical interface between the standard HP-IB
connector and the ribbon cable connector on the A2 controller assembly.
All six RAM ICs (there are only four RAM ICs on newer A2 controller
assemblies) are battery-backed. The battery-backed RAM stores trace
information (two display memory RAMs) and spectrum analyzer state
information (two program RAMs). A total of eight traces and ten states
may be stored. Typical battery life is five years with the lithium battery.
Trace and state information may be retained for up to 30 minutes with
a dead battery and power turned off. This is due to the very low data
retention current of the RAMs.
EEROM
The EEROM stores important amplitude-related correction data. This
includes data for LODA DACs and RF Gain DACs (flatness correction).
The spectrum analyzer serial number, model number, and installed
options are also stored in EEROM.
Firmware
The spectrum analyzer firmware reads the model number and installed
options from the EEROM to determine how to respond to certain
keystrokes.
Display ASM
Much of the miscellaneous digital control is performed by A2U100.
U100 functions as the display ASM (algorithmic state machine) and
character ROM. It also converts the 16-bit CPU data bus to an 8-bit
data bus for the rest of the spectrum analyzer.
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