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Technical Reference Guide www.hp.com 5-9

Input/Output Interfaces

5.4 Serial Interface

Systems covered in this guide may include one RS-232-C type serial interface to transmit and

receive asynchronous serial data with external devices. Some systems may allow the installation

of a second serial interface through an adapter that consists of a PCI bracket and a cable that

attaches to header P52 on the system board. The serial interface function is provided by the

SCH5317 I/O controller component that includes two NS16C550-compatible UARTs.

The UART supports the standard baud rates up through 115200, and also special high speed rates

of 239400 and 460800 baud. The baud rate of the UART is typically set to match the capability

of the connected device. While most baud rates may be set at runtime, baud rates 230400 and

460800 must be set during the configuration phase.

5.4.1 Serial Connector

The serial interface uses a DB-9 connector as shown in the following figure with the pinout listed

in Table 5-7.

Figure 5-3. DB-9 Serial Interface Connector (as viewed from rear of chassis)

The standard RS-232-C limitation of 50 feet (or less) of cable between the DTE (computer) and

DCE (modem) should be followed to minimize transmission errors. Higher baud rates may

require shorter cables.

5.4.2 Serial Interface Programming

Programming the serial interfaces consists of configuration, which occurs during POST, and

control, which occurs during runtime.

Serial Interface Configuration

The serial interface must be configured for a specific address range (COM1, COM2, etc.) and

also must be activated before it can be used. Address selection and activation of the serial

interface are affected through the PnP configuration registers of the SCH5317 I/O controller.

Table 5-7.

DB-9 Serial Connector Pinout

PinSignal Description PinSignal Description

1CD Carrier Detect 6DSR Data Set Ready

2 RX Data Receive Data 7 RTS Request To Send

3 TX Data Transmit Data 8 CTS Clear To Send

4 DTR Data Terminal Ready 9 RI Ring Indicator

5 GND Ground -- -- --

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