Specifications

Chapter 3 Hardware

CoreModule 420 Reference Manual 33

Serial Interface (J3, J9, J13, J14)

The Atlas CPU and Super I/O chips each contain the circuitry for two of the four serial ports. The Atlas

CPU provides serial port 1 (J3) and serial port 2 (J9) through the two independent 10-pin connectors.

The Super I/O chip provides serial ports 3 (J13) and 4 (J14). The serial ports support the following

features:

• Programmable word length, stop bits and parity

• 16-bit programmable baud rate generator

• Interrupt generator

• Loop-back mode

• 16-bit FIFOs for each port

• Ports 1 and 2 are supported by the STPC Atlas processor and are 16540 compatible

♦ Serial 1 (J3, COM1) supports RS-232/RS-485 and has full modem operation

♦ Serial 2 (J9, COM2) supports RS-232/RS-485 and has full modem operation

• Ports 3 and 4 are supported by the Super I/O Controller and are 16550 compatible

♦ Serial 3 (J13, COM3) supports RS-232 with full modem support

♦ Serial 4 (J14, COM4) supports RS-232 with full modem support

NOTE The RS-232/RS-485 mode for Serial Port 1 (COM1) and Serial Port 2

(COM2) are selected in BIOS Setup Utility. However, the RS-232

mode is the default (Standard) for any serial port.

RS-485 mode termination is selected with jumper JP2 Serial 1 (COM1)

and JP1 Serial 2 (COM2) on the module. Refer to Table 2-3 for more

information.

To implement the two-wire RS-485 mode on either serial port, you must tie the equivalent pins together

for the selected port.

For example; you must tie pins 3 (Rx Data –) to 5 (Tx Data –) and pins 4 (Tx Data +) to 6 (Rx Data +) at

Serial Port 1 or 2 (J3 or J9) for the two-wire interface. As an alternate, you may short the equivalent

pins on the DB9 connector attached to respective serial port, as shown in Figure 3-1. Refer also to the

following tables for the specific pins on the connectors. The RS-422 mode uses a four-wire interface

and does not require combining pins for its operation, but you must select RS-485 in BIOS Setup.

CM420RS485jump

Serial Ports (J3, J9)

(COM1 or COM2)

Side View

Standard DB9 Serial

Port Connector (Female)

Rear View

54321

987

Figure 3-1. RS-485 Serial Port Implementation

Table 3-12 provides the signals for the corresponding pins of the two independent serial interface ports

(Serial 1 & 2) and Table 3-13 provides the signals for the corresponding pins of two independent serial

interface headers (Serial 3 & 4).