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Chapter 3
Serial Interfaces (J11, J12)
Two LPC47B272 chips provide the circuitry for the 4 serial ports. One chip provides serial ports 1 and 2
through connector J11 and the second chip provides serial ports 3 and 4 through connector J12. The four
serial ports support the following features:
•
Four individual 16550-compatible UARTs
•
Programmable word length, stop bits and parity
•
16-bit programmable baud rate generator
•
Interrupt generator
•
Loop-back mode
•
Four individual 16-bit FIFOs
• 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
NOTE
The RS232 and RS485/RS422 modes can be selected for any serial port in
BIOS Setup under the BIOS and Hardware Settings menu. However, the
RS232 mode is the default selection (Standard) for any serial port. Refer to
Table 2-5 for termination jumper settings.
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.
Serial A Interface (J11)
for Serial Port 1
(or COM1 Port)
Top View
Table 3-14 gives the pins and corresponding signals for the Serial A interface connector (Serial Ports 1
and 2) and Table 3-15 gives the pins and corresponding signals for the Serial B interface connector
(Serial Ports 3 and 4).
Both Serial A and B connectors have 20 pins, 2 rows, odd/even, (1, 2), with 0.100" pin spacing.
LittleBoard 800
19
9
7
5
3
1
20
10
8
6
4
2
Figure 3-1. RS485 Serial Port Implementation
Reference Manual
Standard DB9 Serial
Or
Port Connector (Female)
Rear View
Hardware
1
2
3
4
5
6
7
8
9
41
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