Addressing - Fluke 9100 Series Service Manual

2/Theory of Operation
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CODE READ
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$F3
$4F
$E1
$14
$FF
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qualified RD- and WR- are also available to the output section. However,
there is a separate data bus for the output section that is selected
when LAT-A7 is low.
Two ICs are required to perform the data bus interfacing: a 74ALS245
Octal 3-State Transceiver (U24) and the 74LS31 delay elements (U29).
Both devices are located on the Main PCA.
The TOPDATA Bus (used by the output section) is isolated from A-D-BUS
(used by the input section) by U24. If a read or write access is made to
any address of the output section (A7 = 0), LAT-A7 remains low, thereby
providing an enable signal to U24 pin 19 (G-). The WR- signal determines
the direction of data travel. If WR- is high, the data passes from the
TOPDATA bus to A-D-BUS for a read. If WR- is low, the data passes in the
other direction for a write.
Some register control signals (such as COMMAND0- and COMMAND1- for U5
and U6 of the Top PCA) use the rising edge of WR- to latch data. Since
the WR- signal also controls the direction of the TOPDATA bus through
}U24, U29 provides a nominal 46.5 ns delay to the direction control
signal (WR-DLY-) on U24. This insures that, during accesses to the
output section, the data bus is held in the correct direction by U24
while the rising edge of RD- or WR- latches the data.

ADDRESSING

All addresses with A7 low are reserved for the output section. Since A3
through A1 only go to the custom chips for use as addresses and STROBE-
is only active for addresses with LDS- active (address bit 0 = 1), the
address space is effectively limited to $DOX01 through $DOX71.
Table 2-6 lists the output section addresses and the signals (or
registers) that are affected by accessing the address for both reads and
writes.
Performing a write to $DOX01 causes the COMMAND0- output of U10 (Top
PCA) to toggle, thereby latching the data on the bus into the U5
register. (See the heading, "Output Control Functional Block", further
on in this section for more information.) When a read is performed at
this address, the Vector Drive Status Nybble is returned from U25 (Main
PCA). (See the heading, "Drive Status Functional Block", further on in
this section and Table 2-10 for more information.)
Table 2-5. Connector Code Examples
MEANING
No clip on B side, 20-pin clip on A side
24-pin clip on B side, no clip on A side
40-pin clip installed
16-pin clip on B side, 24-pin clip on A side
No clips installed
2-18