Rockwell Automation T3151 ICS Regent Real time Clock Communications Modules - Manual (Page 2)

Real-Time Clock Communications Modules (T3151)
2
Industrial Control Services
Each real-time clock communications module has a Z80 micro-
processor, a PROM containing all of the module’s executable
software, static RAM containing program variables, the real-
time clock, shared RAM for transferring information between
the processor modules and the communications module’s
microprocessor, and a dual-channel UART with RS-232 serial
port interfaces. Both the clock and the static RAM are
battery-backed. If the system is powered down the battery
continues to keep the clock running. The microprocessor
reads the time, checks it for consistency, and then transfers it
to the shared RAM where it can be read by the processor
modules.
Each communications module receives power from all three of
the processor modules. A power-sharing circuit in each of the
communications modules receives the power from the three
processor modules and combines it through a diode OR power-
sharing circuit. This ensures that if one processor module's
power supply fails, the communications module will continue
to operate by drawing power from the two remaining power
supplies, and the system's communications functions are
maintained.
The Dual UART (universal asynchronous receiver/trans-
mitter) buffers incoming and outgoing communications
characters. The triplicated processor modules interrupt once
every millisecond to read characters from or write characters
to the communications module.