Chapter 5 Input/Output Interfaces
5-6 Compaq iPAQ Series of Desktop Personal Computers
Second Edition – February 2001
5.4 SERIAL INTERFACE
The legacy models include a serial interface to transmit and receive asynchronous serial data with
external devices. The serial interface function is provided by the I/O controller component that
includes a NS16C550-compatible UART.
NOTE: Legacy-free models do not have an externally accessible serial port, but do have
serial interface logic to satisfy the serial port requirements of some operating systems.
The iPAQ2.0 and legacy-free iPAQ 1.x systems also includes a serial test header on the
system board.
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 RS-232 INTERFACE
On the legacy system, the UART is associated with a DB-9 connector that complies with EIA
standard RS-232-C. The DB-9 connector is shown in the following figure and the pinout of the
connector is listed in Table 5-5.
Figure 5-3. Serial Interface Connector (Male DB-9 as viewed from rear of chassis)
Table 5–5. DB-9 Serial Connector Pinout
Table 5-5.
DB-9 Serial Connector Pinout
Pin Signal Description Pin Signal Description
1 CD Carrier Detect 6 DSR 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 -- -- --
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.
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