Ampro Corporation MightyBoard 821 manual Serial Interfaces, RS485 Serial Port Implementation

Chapter 3 Hardware

Serial Interfaces

The Super I/O (W83627HF) chip and the LPC UART controller (F81216D) provide the circuitry for the four serial ports. The Super I/O chip provides serial ports 1 and 2 through connector J3 and header J6 respectively. The LPC UART controller provides serial ports 3 and 4 through header J15. 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 Ports 1 and 2

♦Serial Port 1 (COM1) supports RS232 and full modem support

♦Serial Port 2 (COM2) supports RS232, full modem support, and IrDA

•Serial B Interface

♦Serial Port 3 (COM3) supports RS232/RS485/RS422 and full modem support

♦Serial Port 4 (COM4) supports RS232/RS485/RS422

NOTE The RS232/RS485/RS422 modes are selected in BIOS Setup under BIOS and Hardware Settings menu for Serial ports 3 (COM3) and 4 (COM4). However, the RS232 mode is the default (Standard) for any serial port.

RS485 mode termination is selected with jumper JP3, pins 1-2 (COM3), and pins 3-4 (COM4), when the RS485 mode is selected in BIOS Setup.

To implement the two-wire RS485 mode on serial ports 3 or 4, you must tie the equivalent pins together for the selected port.

For example, on Serial Port 3, tie pins 3 to 5 and pins 4 to 6 at the Serial B interface connector as shown in Figure 3-1. As an alternate, tie pins 2 to 3 and pins 7 to 8 at the DB9 serial connector for serial port 3 as shown in Figure 3-1. Refer to the following tables for the specific pins for serial ports 3 and 4 on the serial B connector. The RS422 mode uses a four-wire interface and does not need any pins tied together, but you must select RS485 mode in BIOS Setup.

Serial B Interface (J15)	19	9 7 5 3 1	1	2	3	4	5
		Or	Standard DB9 Serial
for Serial Port 3			Port Connector (Female)
(or COM3 Port)	20	10 8 6 4 2	Rear View
Top View
				6	7	8	9

Figure 3-1. RS485 Serial Port Implementation

MB821_RS485

Table 3-4lists the pin-outs for the Serial Port 2 (COM 2) interface header (J6) . Table 3-4lists the pin-outs for Serial Ports 3 and 4 (COM 3 and COM 4) interface header (J15).

18 Reference Manual MightyBoard 821