Distributor of Digi International: Excellent Integrated System Limited
Datasheet of XC09-038PKC-R - MODEM RF 900MHZ RS232/485
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9XCite
‐
PKG
‐
R™
RS
‐
232/485
RF
Modem
–
Product
Manual
v2.1
[2007.01.04]
©
2007
MaxStream,
Inc.
12
3.
RF
Modem
Operation
3.1. Serial Communications
3.1.1. RS-232 and RS-485/422 Data Flow
The XCite RF Modem can enable a host device to communicate wirelessly. To transmit, the host
device simply sends serial data to the XCite RF Modem pins. The RF modem then converts the data
into FCC-approved RF data. Once transmitted, the RF data can be detected by receiving XCite RF
Modems, checked for integrity and then sent to a receiving device.
Figure
3
‐
01. Data
Flow
in
RS
‐
232
and
RS
‐
485/422
environments.
(Low
‐
asserted
signals
distinguished
with
a
horizontal
line
over
signal
name.)
3.1.2. Serial Data
Data enters the MaxStream RF modem through the DI Pin as an asynchronous serial signal. The
signal should idle high when no data is being transmitted.
The UART performs tasks (such as timing and parity checking) needed for communication. Serial
communication consists of two UARTs which must be configured with compatible parameters
(Baud rate, parity, start bits, stop bits, data bits) to have successful communication. Each data
packet consists of a start bit (low), 8 data bits (least significant bit first) and a stop bit (high). The
following figure illustrates the serial bit pattern of data passing through the modem.
Figure
3
‐
02. Serial
(UART)
data
packet
0x1F
(decimal
ʺ
31
ʺ
)
as
transmitted
through
the
XCite
Module
Data
Format
is
8
‐
N
‐
1
(8
bits
‐
No
Parity
‐
1
Stop
Bit)
In the example above, the MaxStream RF modem transfer 8 bits over-the-air [Selectable using BI
(Number of Bits) Parameter]. Start and stop bits of the UART signal are not transmitted over-the-
air, but are regenerated by the receiving modem
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