General - Motorola R-2001A Service Manual

14-1. General. Remote control of the system is possible using a IEEE-488 bus and the IEEE Interface
Module. The Interface Module provides the interface for the 488 bus and provides for processor control of most
of the functions normally controlled from the front panel. A block diagram of the IEEE Interface Module is
shown in figure 14-1 with its schematic shown in figure 14-2. See section 22 for information on the use of the
IEEE Bus for system control.
14-2. IEEE Bus Interface. Bus buffering and interface protocol as defined by the IEEE-488 specification is
provided for by.the IEEE Bus I nterface circuit. The system processor accesses the interface directly through its
address', data, and control buses for reading from or writing to the IEEE bus.
14-3. RF Level Control. The RF Level Control circuitry selects between the 5 VDC + AM MOD or the AM
MOD + DCREF(I) input for remote or local control respectively. For remote control the 5 VDC + AM MOD input
is electronically attenuated to provide the requested RF output level. For local control the attenuator is
programmed for unity gain so that the AM MOD + DC REF (I) signal from the front panel RF level potentiometer
controls the RF output level.
14-4. For the IEEE control option, a electronically programmable RF step attenuator is installed in the
system. Control of the attenuator is then from the processor through the Address Decode and Control Latch
circuitry on the Interface Module.
14-5. Modulation Control. Each of the three modulation sources are individually controllable by the IEEE
Bus Interface module. For remote control the respective modulation input (INT MOD (I), EXT MOD (I), and
1 kHz SINE) is switched to a programmable attenuator. The system processor selects the level of attenuation
necessary to provide the requested level of modulation. For local control the attenuators are programmed for
unity gain and the respective modulation signal from the front panel level control (INTMODRTN (I), EXT MOD
RTN (I), and 1 kHz SINE RTN (I)) is selected to the attenuator to provide modulation level control.
14-6. Address Decode and Control Latches. The system processor has direct control over the
programmable attenuators on the module with the Address Decode and Control Latch circuitry. Control data
on the data bus (DO-D7) is latched at the Control Latch indicated by the address bus (AO-A15).
SECTION 14
IEEE INTERFACE MODULE (A8)
14-1