10 Freescale Semiconductor
Use of the J1 connector to input RS-232 signals requires disabling the on-board RS-232
transceiver. Otherwise, signal corruption may occur. Disabling the on-board transceiver is
accomplished by opening cut-traces CT1, and CT2. Simply remove the circuit trace between
the cut-trace pads to open the circuit. To restore the circuit functionality, install a 1206 size, 0-
ohm, resistor or a short piece of wire across the cut-trace pads.
Table 1: Serial COM Signals
COM Signal
MCU Port
Connector
Disable
TXD PS1/TXD
J1-5
CT5
RXD PS0/RXD
J1-7
CT4
COM Connector
A standard 9-pin D- Sub connector provides external connections for the COM port. The COM
port is configured as a DCE device. Component U2 provides RS-232 translation services.
The figure below shows the DB9 connector.
Figure 2: COM Connector
1
6
TXD
2
7
RTS
RXD
3
8
CTS
4
9
NC
GND
5
Female DB9 connector that interfaces to the DCE serial port via an
RS232 transceiver. It provides simple 2-wire asynchronous serial
communications without flow control. A straight-through serial cable may
be connected to a DTE device such a PC
Pins 1, 4, and 6 are connected together.
