Loop Control Functional Block - Fluke 9100 Series Service Manual

The Vector Control RAM Functional Block consists of an 8K x 8 SRAM
(U600), a 74AC273 Octal D-Type Flip-Flop (U601), a resistor pack (Z600),
and one 74AC08 AND gate (U19).
The Z600 resistor pack provides isolation from the D-BUS data bus. When
only U600 has been selected to be written to, the data on the bus passes
through Z600 and is input to U600. When vectors are driven and all
devices have been selected, the resistor pack provides enough isolation
from the bus to prevent other devices from interfering with the output
of the U600 RAM.
When Vector RAM is being loaded (i.e., DRV/LD- is low), the output of
U601 is cleared to prevent the control signals from causing erratic
behavior in the module.
When vector driving occurs, the current data out of U600 is latched in
U601 by LAT-CLK. The outputs of U601 are used for the following
purposes:
o DONEDRV - terminates vector driving when the final vector in the
o HSOUT - suspends vector driving until the programmed edge is
o LOOP - decrements the loop counter and checks the results after
o BOTH - loops until the loop count is exhausted and then
o CAP-CLK - clocks the input section in the center of the current
When the TP5 TST test point is pulled low (for testing purposes), the
output of U601 is disabled (forced low). This permits the control RAM to
be loaded with test patterns and driven without affecting the output
(i.e. LOOP bits do not force looping). CRCs of the RAM output verify
that the proper data is at the proper address.

Loop Control Functional Block

All the loop control circuitry is located on the Main
PCA unless otherwise noted.
When a vector file that uses looping is loaded into the module, several
actions are performed. A write is performed to $D0X21 to clear LTCCLR-
(bit 2), which causes the U25 PAL to reset the LOOP-DONE output on U28.
Next, a write is performed to $D0X21 with bit 3 set or cleared, choosing
the loading of either the MSB or LSB of the loop count number contained
in the vector file (the value loaded is actually count -- 2). Then a
write is performed to $D0X31 with the MSB or LSB as appropriate. This
file is driven.
detected on the WAIT input.
reaching one vector prior to the ENDLOOP statement.
terminates vector driving.
vector period.
NOTE
2-27
2/Theory of Operation