User`s manual

12 RabbitCore RCM3000
2.2 Serial Communication
The RCM3000 Series 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.
2.2.1 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 additional 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
synchronously clocks the data in or out. Either of the two communicating devices can sup-
ply the clock. When the Rabbit 3000 provides the clock, the baud rate can be up to 80% of
the system 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.
2.2.2 Ethernet Port
Figure 4 shows the pinout for the RJ-45 Ethernet port (J4). Note that some Ethernet con-
nectors are numbered in reverse to the order used here.
Figure 4. RJ-45 Ethernet Port Pinout
Two LEDs are placed next to the RJ-45 Ethernet
jack, one to indicate an Ethernet link (LNK) and one
to indicate Ethernet activity (ACT).
The Ethernet signals are also available 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 5.
The RJ-45 connector is shielded to minimize EMI
effects to/from the Ethernet signals.
ETHERNET
RJ-45 Plug
1. E_Tx+
2. E_Tx
3. E_Rx+
6. E_Rx
1
8
RJ-45 Jack
Figure 5. Isolation Resistor R31
RJ-45 Ethernet Plug
R31
Chassis
Ground
Board
Ground