Rockwell Automation MSR04XI Serial Communications Module RS232 - Manual (Page 9)

MSR04XI October 2005 – Issue 8 9
Triguard SC300E MSR04XI Serial Communications Module RS232
Figure 2-2 Serial communications cable wiring
THEORY OF OPERATION
Triplicated data enters and leaves the module (Figure 2-3 ) via the chassis backplane
connector J1 and is isolated from the MPP by bus transceivers. Data for transmission is
loaded into dual port RAM in each of the three circuit branches and is voted 2-oo-3 before being
passed to the USARTs on the daughter board where it is serialised and sent to the appropriate
communications port.
Data received at the ports is converted to parallel form by the USART and written to dual port
RAM in each branch, the data is accompanied by information about the status of the ports and
the embedded microprocessor. The dual port memory is then read by the MPP via a second
set of transceivers.
The four communications ports are configured to run in full duplex mode using an RS232
interface and having a maximum rate of 19200 Baud. The communications ports are isolated
from the module circuits by opto-isolators and connected to field connector J2 at the rear of the
module. The ports are capable of powering modems or line drivers for transmission over long
distances.
Power for the module circuits is derived from the dual redundant SC300E power supply units,
individual auctioneering and regulating circuits supplying various logic areas. The
communications port opto-isolators and interfaces also have separate supplies.