User's Manual

DE910 Series Hardware User Guide
1vv0301183 Rev.1 – 2015-2-13
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Reserved. Page 45 of 70
8.1. Modem Serial Port 1
Serial port 1 on the DE921 is a +1.8V UART with all 7 RS232 signals.
It differs from the PC-RS232 in the signal polarity (RS232 is reversed) and levels.
Pin Signal I/O Function Type
F20
DCD O Data Carrier Detect 1.8V
G21
RXD O Transmit line *see Note 1.8V
J21
TXD I Receive line *see Note 1.8V
K20
DTR I Data Terminal Ready 1.8V
H20
DSR O Data Set Ready 1.8V
E21
RTS I Request to Send 1.8V
C21
CTS O Clear to Send 1.8V
L21
RI O Ring Indicator 1.8V
The following table shows the typical input value (pulled inside the baseband chipset) and
status for input lines all module states:
Signal/State OFF RESET ON Powersaving PU tied to
TXD
unknown
PD:
21K~210K
PU:
39K~390K
PU:
39K~390K
1.8V
RTS
PD:
21K~210K
DTR
PU:
39K~390K
NOTE:
For minimum implementation, only the TXD and RXD lines must be connected, the other
lines can be left open provided a software flow control is implemented.
NOTE:
In order to avoid a back powering effect it is recommended to avoid having any HIGH logic
level signal applied to the digital pins of the DE921 when the module is powered off or during
an ON/OFF transition.