Rabbit RabbitCore RCM2200, Руководство пользователя

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User’s Manual 23
4.2 Serial Communication
The RCM2200 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
RCM2200 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
64. 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 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 2000 provides the clock, the baud rate can be up to 80% of the
system clock frequency divided by 128, or 138,240 bps for a 22.1 MHz clock speed.
Serial Port A is available only on the programming port, and so is likely to be inconve-
nient to interface with.
4.2.2 Ethernet Port
Figure 6 shows the pinout for the RJ-45 Ethernet port (J2). Note that some Ethernet con-
nectors are numbered in reverse to the order used here.
Figure 6. 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 J4.
The
ACK and LNK signals can be used to drive LEDs
on the user board the RCM2200 is connected to.
The transformer/connector assembly ground is con-
nected to the RCM2200 printed circuit board digital
ground via a 0
Ω
resistor, R29, as shown in Figure 7.
Figure 7. Isolation Resistor R29
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
R29
Chassis
Ground
Board
Ground