Advantech SOM-ETX Design Guide
•
Trace lengths must always be as short as possible (must be less than 1 inch).
•
Make trace lengths as equal as possible.
•
Keep Tx and Rx differential pair’s routes separated (at least 0.02-inch
separation). Better to separate with a ground plane.
•
Avoid routing Tx and Rx traces over or under a plane. Areas under the Tx and
Rx traces should be open.
•
Use precision components in the line termination circuitry ~1 percent.
5.9 Serial Port(Com1/Com2)
SOM-ETX provides two serial ports, each are programmable of character lengths (5,
6, 7, 8), parity bit generation and detection (even, odd, or no parity bit), and baud rate
generator. Different INTs and I/O addresses are also selectable if BIOS supports.
5.9.1 Signal Description
Table 5.19 Serial Bus signals description
Pin Signal I/O Description
C87 DTR#1
C69 DTR#2 O
Data Terminal Ready. An active low signal informs the modem or data
set that controller is ready to communicate.
C97 RI#1
I
C79 RI#2
I
C95 TXD1
O
C77 TXD2
O
Serial Output. Used to transmit serial data out to the communication
link.
C83 RXD1
I
RXD2
I
Serial Input. Used to receive serial data through the communication link.
C93 CTS#1 I
C75
Clear To Send. An active low signal notifies the UART when the modem
is ready to receive data.
C85 RTS#1 O
C67
Request To Send. An active low signal informs the modem or data set
that the controller is ready to send data.
C89 DCD#1 I
C71 DCD#2 I
Data Carrier Detect. An active low signal indicates the modem or data
set has detected a data carrier.
C91 DSR#1 I
C73 DSR#2 I
Data Set Ready. An active low signal indicates the modem or data set is
ready to establish a communication link.
Table 5.19 shows SOM-ETX Serial bus signals, including pin number, signals, I/0,
power plane, terminal resistors, damping resistors and descriptions.
O
Ring Indicator. An active low signal indicates that a ring signal is being
received from the modem or data set.
C63
CTS#2 I
RTS#2 O
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Chapter 5 Carrier Board Design Guidelines
