Specifications

Chapter 3 Hardware
22 Reference Manual LittleBoard 800
• Serial A Interface (J11)
♦ Serial Port 1 (COM1) supports RS232/RS485/RS422 and full modem support
♦ Serial Port 2 (COM2) supports RS232/RS485/RS422
• Serial B Interface (J12)
♦ Serial Port 3 (COM3) supports RS232/RS485/RS422 and full modem support
♦ Serial Port 4 (COM4) supports RS232/RS485/RS422
To implement the two-wire RS485 mode on any serial port, you must tie the equivalent pins together for
each port.
For example, on Serial Port 1, tie pin 3 to 5 and pin 4 to 6 at the Serial A interface connector (J11) as shown
in Figure 3-1. As an alternate, tie pin 2 to 3 and pin 7 to 8 at the DB9 serial connector for Serial Port 1 as
shown in Figure 3-1. Refer also to the following tables for the specific pins for the other ports on each
connector. The RS422 mode uses a four-wire interface and does not need any pins tied together, but you
must select RS485 in BIOS Setup.
Figure 3-1. RS485 Serial Port Implementation
Table 3-5 Defines the pins and corresponding signals for the Serial A interface connector (Serial Ports 1 and
2) and Table 3-6 defines the pins and corresponding signals for the Serial B interface connector (Serial Ports
3 and 4).
Both Serial A and B headers use 20 pins, 2 rows, odd/even, (1, 2), with 0.100" pitch.
NOTE The RS232 and RS485/RS422 modes can be selected for any serial port in BIOS
Setup under the Advanced menu. However, the RS232 mode is the default
selection (Standard) for any serial port.
Table 3-5. Serial A Interface Pin/Signal Descriptions (J11)
Pin # Pin #
DB9
Signal Description
11
(COM1)
DCD1
*
Data Carrier Detect 1 – Indicates external serial communications device
is detecting a carrier signal (i.e., a communication channel is currently
open). In direct connect environments, this input will be driven by DTR1
as part of the DTR/DSR handshake.
2 6 DSR1* Data Set Ready 1 – Indicates external serial communications device is
powered, initialized, and ready. Used as hardware handshake with DTR1
for overall readiness to communicate.
3 2 RXD1
RX1-
Receive Data 1 – Serial port 1 receive data in.
RX1- – If in RS485 or RS422 mode, this pin is Receive Data 1 -.
47RTS1*
TX1+
Request To Send 1 – Indicates Serial port 1 is ready to transmit data.
Used as hardware handshake with CTS1 for low level flow control.
TX1+ – If in RS485 or RS422 mode, this pin is Transmit Data 1 +.
53TXD1
TX1-
Transmit Data 1 – Serial port 1 transmit data out.
TX1- – If in RS485 or RS422 mode, this pin is Transmit Data 1 -.
Serial A Interface (J11)
for Serial Port 1
(or COM1 Port)
1
2
3
4
5
6
7
8
9
10
20
19
Top View
5
4
32
1
9
8
7
6
Standard DB9 Serial
Port Connector (Female)
Rear View
Or