Theory Of Operation; Pcb Assemblies - Racal Instruments 1260-64 Manual

User Manual 1260-64
Chapter 5

THEORY OF OPERATION

The 1260-64 consists of three PCB Assemblies. The smallest is

PCB Assemblies

used only to mount connector J 1 to the front panel. The other
small PCB Assembly is required to pass the local bus signals,
LBUSO through LBUS 11, through the unused second slot of
this double-wide module. The VXI IACK and BUS GRANT 0
through 3 signals are jumpered to allow the PCB Assembly to
be used in autoconfiguring backplanes.
The main logic PCB Assembly contains DC relay banks, 1260
Local Bus interface circuitry, and drivers for both the relay bank
and the RE relays. The VXI interface is described in the Theory
of Operation section of the 1260 Series VXI Switching Cards
Manual. The relay driver circuitry is contained in monolithic IC
driver chips. The relay banks are shown in Figures 4-3 through
4-6. Not shown in these figures are internal clamp diodes.
These diodes will clamp minor inductance effects, such as
those caused by wiring; but they are not intended to replace
suppression diodes across the solenoid coils of external relays,
or other inductive loads. Referring to the schematic diagram, the
diodes between the Contact lines and ground clamp switch-to-
open transients when the bank is used as a source driver. The
diodes between the Contact lines and the External B+ clamp
switch-to-open transients when the bank is used as a sink
driver.
Theory of Operation 5-1