HP X09 Manuál stáhnout pdf (Strana 14)

XStream‐PKG‐E™EthernetRFModem–ProductManualv5.x00[2006.02.24]

Figure3‐02. DataTransmissionSequenceÆ

After either RB or RO conditions are met,

the modem then initializes a

communications channel. [Channel

initialization is the process of sending an

RF initializer that synchronizes receiving

modems with the transmitting modem.

During channel initialization, incoming

serial data accumulates in the DI buffer.]

Serial data in the DI buffer is grouped

into RF packets [refer to PK (RF Packet

Size)]; converted to RF data; then

transmitted over-the-air until the DI

buffer is empty.

RF data, which includes the payload data, follows the RF initializer. The payload includes up to

the maximum packet size (PK Command) bytes. As the transmitting modem nears the end of the

transmission, it inspects the DI buffer to see if more data exists to be transmitted. This could be

the case if more than PK bytes were originally pending in the DI buffer or if more bytes arrived

from the UART after the transmission began. If more data is pending, the transmitting modem

assembles a subsequent packet for transmission.

RF Data Packet

The RF packet is the sequence of data used for communicating information between MaxStream

Modems. An RF Packet consists of an RF Initializer and RF Data.

Figure3‐03. RFDataPacketComponents

* When streaming multiple RF packets,

the RF Initializer is only sent in front of the

first packet.

RF Initializer

An RF initializer is sent each time a new connection sequence begins. The RF initializer contains

channel information that notifies receiving modems of information such as the hopping pattern

used by the transmitting modem. The first transmission always sends an RF initializer.

An RF initializer can be of various lengths depending on the amount of time determined to be

required to prepare a receiving modem. For example, a wake-up initializer is a type of RF

initializer used to wake remote modems from Sleep Mode (Refer to the FH, LH, HT and SM

Commands for more information). The length of the wake-up initializer should be longer than the

length of time remote modems are in cyclic sleep.

Header

The header contains network addressing information that filters incoming RF data. The receiving

modem checks for a matching Hopping Channel (HP parameter), Vendor Identification Number

(ID parameter) and Destination Address (DT parameter). Data that does not pass through all

three network filter layers is discarded.

CRC (Cyclic Redundancy Check)

To verify data integrity and provide built-in error checking, a 16-bit CRC (Cyclic Redundancy

Check) is computed for the transmitted data and attached to the end of each RF packet. On the

receiving end, the receiving modem computes the CRC on all incoming RF data. Received data

that has an invalid CRC is discarded [Refer to the Receive Mode section, next page].

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