Connector Code Functional Block; Input Protection Functional Block; Output Section Theory Of Operation - Fluke 9100 Series Service Manual

2/Theory of Operation
the full-size module plugs into both connectors (both J1 and J2 on the
Top PCA). Together, the clip(s) plugged into both J1 and J2 of the Top
PCA generate an 8-bit code that can be decoded by the mainframe to
identify the size of the installed clip module(s).
Fuse Blown Detection
Detection of blown fuses is performed by two LM324 Op-Amps (U2) and one
part of U3 configured as a window detector. If the XGND signal exceeds a
+100 millivolt window, U3-6 will go low, forcing the FUSEDET line to go
high. When the interrupt register is read (READ 0 $DXXDX), a 1 in bit 3
indicates the fuse is blown. This blown fuse indication is cleared by
writing to the I/O Command Register (WRITE 0 $DXXDX) with a data value
that has bit 3 = 0.

Connector Code Functional Block

The components associated with the Connector Code block are the 74HCT244
Octal Buffer/Line Driver (U16) and part of the J2 and J3 connectors.
This block is located on the Main PCA as indicated on the functional
block diagram shown in Figure 2-1.
The mainframe determines which Clip Module the user has installed by
reading and decoding connector codes encoded in each Clip Module. To
read the code, the mainframe performs a read at $DXXE1. This operation
generates the ADE- signal, which in turn enables U16, placing the code
on the data bus. Of the eight bits read, the lower four bits refer to
the "A side", and the upper four bits refer to the "B side". Thus,
differentiation is possible for 16 different conditions on each side of
the module. Clips that use up an entire module use an 8-bit code. The
most significant nybble of these codes is 1110. A list of these codes is
shown in Table 2-4. For example, to determine the connector codes on
module 3, a Read 0 $D04E1 should be performed. Table 2-5 presents some
examples of codes and their interpretation.

Input Protection Functional Block

The input protection circuit clamps overvoltage, undervoltage, and
static conditions before they reach the custom chip. The signals from
the I/O lines enter the Main PCA through connectors J2 and J3. Each line
passes through a 100 ohm current-limiting resistor. The lines are then
routed to the custom chip inputs. Also attached to the lines are BAV99
diode packs; one diode is tied to +5 volts and the other is tied to
ground to clamp any input above +5 volts or below ground.

OUTPUT SECTION THEORY OF OPERATION

All the output section circuitry is located on the Top
PCA unless otherwise indicated.
NOTE
2-16