Serial Communication; Serial Ports; Ethernet Port - Rabbit RCM3000 User Manual

4.2 Serial Communication

The RCM3000 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
RCM3000 is mounted on. For example, the Prototyping Board has a standard RS-232
transceiver chip.

4.2.1 Serial Ports

There are six serial ports designated as Serial Ports A, B, C, D, E, and F. All six serial ports
can operate in an asynchronous mode up to the baud rate of the system clock divided by 16.
An asynchronous port can handle 7 or 8 data bits. A 9th bit address scheme, where an addi-
tional bit is sent to mark the first byte of a message, is also supported. Serial Ports A, B, C,
and D can also be operated in the clocked serial mode. In this mode, a clock line synchro-
nously clocks the data in or out. Either of the two communicating devices can supply the
clock. When the Rabbit 3000 provides the clock, the baud rate can be up to 80% of the sys-
tem clock frequency divided by 128, or 183,750 bps for a 29.4 MHz clock speed.
Serial Ports E and F can also be configured as SDLC/HDLC serial ports. The IRDA proto-
col is also supported in SDLC format by these two ports.
Serial Port A is available only on the programming port.

4.2.2 Ethernet Port

Figure 7 shows the pinout for the
RJ-45 Ethernet port (J4). Note that
some Ethernet connectors are num-
bered in reverse to the order used
here.
Two LEDs are placed next to the
RJ-45 Ethernet jack, one to indicate
an Ethernet link (
indicate Ethernet activity (
The Ethernet signals are also avail-
able on header J1.
The transformer/connector assembly ground is con-
nected to the RCM3000 printed circuit board digital
ground via a 0 Ω resistor, R31, as shown in
Figure 8.
The RJ-45 connector is shielded to minimize EMI
effects to/from the Ethernet signals.
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ETHERNET
Figure 7. RJ-45 Ethernet Port Pinout
RJ-45 Ethernet Jack
Board
Ground
Figure 8. Isolation Resistor R31
1
8
1. E_Tx+
2. E_Tx–
3. E_Rx+
6. E_Rx–
R31
Chassis
Ground
RabbitCore RCM3000