A2 Display Pca Circuit Description; Main Pca Connector - Fluke 2640A Service Manual

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The input (XTI) is then routed to the FPGA (A1U31), that contains the External Trigger
control circuitry. The Microprocessor sets control register bits in the FPGA (A1U31) to
control the external trigger circuit. The External Trigger control circuit output
(A1U31-9) drives an interrupt input on the Microprocessor (A1U1-121).
If External Triggering is enabled (see User Manual), the Microprocessor sets FPGA
control register bits to allow a low level on the TGIN* input to cause the External
Trigger Interrupt (XTINT*; A1U31-9) to go low. The Microprocessor then changes the
FPGA control register bits to allow a high level on the TGIN* input to cause XTINT*
(A1U31-9) to go low. Thus the Microprocessor can detect both rising and falling edges
on the TGIN* input. Normally, the XTINT* output of the FPGA (A1U31-9) should be
low only for a few microseconds at any time. If it is held low constantly, the instrument
does not operate. Resistor A1R39 pulls the XTINT* output high to ensure that it is high
during power-up.
The instrument has a trigger output line that is pulsed low when the Microprocessor
writes a bit to a register in the FPGA (A1U31). The trigger output line (TGOUT*
A1J6-3) is pulsed low for 250 to 500 microseconds at the beginning of the first
measurement of each acquisition scan. The pulse width is set by circuitry within the
FPGA. The output circuitry for the trigger output is the same as for the digital and alarm
output buffers, except for transistor A1Q10. This transistor is used to increase the
amount of current the trigger output can sink. This allows the trigger output to drive the
trigger inputs of up to 19 instruments.

A2 Display PCA Circuit Description

Display Assembly operation is classified into six functional circuit blocks as follows:
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Each circuit block is described in the following paragraphs.

Main PCA Connector

The 20-pin Main PCA Connector (A2J1) provides the interface between the Main PCA
and the other functional blocks on the Display PCA. Seven of the connector pins provide
the necessary connections to the four power supply voltages: -30V dc, -5V dc (Vee),
+4.9V dc (Vcc), and 5.4V ac filament voltage (see Table 2-4). Six pins are used to
provide the interface to the Front Panel Switches (A2SWR1 through A2SWR6). The
other seven signals interface the Microprocessor (A1U4) to the Display Controller
(A2U1) and pass the reset signals between the assemblies.
2-26

Main PCA Connector

Front Panel Switches
Display
Beeper Drive Circuit
Watchdog Timer/Reset Circuit
Display Controller
2-48.
2-49.