User`s manual

User’s Manual 29
4.2 Serial Communication
The RCM2100 board does not have an RS-232 or an RS-485 transceiver directly on the
board. However, an RS-232 or RS-485 interface may be incorporated on the board the
RCM2100 is mounted on. For example, the Prototyping Board supports a standard
RS-232 transceiver chip.
4.2.1 Serial Ports
There are four serial ports designated as Serial Ports A, B, C, and D. All four serial ports
can operate in an asynchronous mode up to the baud rate of the system clock divided by
32. An asynchronous port can handle 7 or 8 data bits. A 9th bit address scheme, where an
additional bit is sent to mark the first byte of a message, is also supported. Serial Ports A
and B can be operated alternately in the clocked serial mode. In this mode, a clock line
synchronously clocks the data in or out. Either of the two communicating devices can sup-
ply the clock. When the Rabbit 2000 provides the clock, the baud rate can be up to 1/4 of
the system clock frequency, or 5.52 Mbps for a 22.1 MHz clock speed.
4.2.2 Ethernet Port
Figure 7 shows the pinout for the RJ-45 Ethernet port (J4). Note that there are two stan-
dards for numbering the pins on this connector—the convention used here, and numbering
in reverse to that used here.
Figure 7. RJ-45 Ethernet Port Pinout
The transformer/connector assembly ground is con-
nected to the RCM2100 printed circuit board digital
ground via a 0 Ω resistor “jumper,” R5, as shown in
Figure 8.
The factory default is for the 0 Ω resistor “jumper” at
R5 to be installed. In high-noise environments, it may
be useful to ground the transformer/connector assem-
bly directly through the chassis ground. This will be
especially helpful to minimize EMI problems.
Figure 8. Isolation Resistor R5
ETHERNET
RJ-45 Plug
1. E_Tx+
2. E_Tx
3. E_Rx+
6. E_Rx
1
8
RJ-45 Jack
RJ-45 Ethernet Plug
R5
Chassis
Ground
Board
Ground