Digi 9XCite-PKG Manuel télécharger pdf (Page 12)

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ʺ31ʺ)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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