XStream™ Advanced Programming & Configuration

XStream Advanced Programming & Configuration – Advanced Manual v4.2A
Transmit Mode
When the first byte of serial data comes through the DI Pin and arrives in the DI Buffer, the
module transitions into Transmit Mode. Once in Transmit Mode, the module initializes a
communications channel. During channel initialization, incoming serial data accumulates in the DI
buffer. Once the channel is initialized, data in the DI buffer is grouped into packets (up to 64
bytes in each packet) and is transmitted. The module continues to transmit data packets until the
DI buffer is empty. Once transmission is finished, the module returns to Idle Mode. This
progression is shown below.
Figure 14.
Transmission of data
Data Received in
Data Buffer
Begin
Initialization of
Communications
Channel
Idle
Mode
not complete
Collect Serial
Data in
Data Buffer
Initialization Complete
RF OUT Buffer
not empty
Send Data &
Assert TX/PWR
when < 17
bytes left
Remained Data
in DI Buffer
No Data in
DI Buffer
RF OUT Buffer Empty
De-Assert
TX/PWR
[Also refer to the block diagram of the XStream OEM RF Module located in the “XStream OEM RF
Module” Product Manual]
Cyclic Redundancy Check (CRC)
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 data packet before
transmission. On the receiving end, the receiver computes the CRC on all incoming data.
Received data that has an invalid CRC is discarded [See “Receive Mode” section on next page].
Transmission Latency
Transmission latency is dependent on the number of bytes contained in a packet and the baud
rate of the XStream Module. A wake-up initializer is sent every time a new transmission sequence
begins. In some applications, SY Command can be used to reduce the length of the wake-up
initializer (contains channel information used to initialize listening receivers to the transmitter’s
hopping pattern) sent at the beginning of a transmission and thus reduce latency.
© 2004 MaxStream, Inc., Confidential and Proprietary 16