Product manual

XStream-PKG-R™ RS-232/485 RF Modem – Product Manual v5.x00

3.2. Modes of Operation

XStream RF Modems operate in five modes.

Figure 3.3. XStream Modes of Operation

Modem can only be in one mode at a time.

3.2.1. Idle Mode

When not receiving or transmitting data, the modem is in Idle Mode. The modem uses the same

amount of power in Idle Mode as it does in Receive Mode.

The modem shifts into the other modes of operation under the following conditions:

• Serial data is received in the DI Buffer (Transmit Mode)

• Valid RF data is received through the antenna (Receive Mode)

• Command Mode Sequence is issued (Command Mode)

• Sleep Mode condition is met (Sleep Mode)

After responding to any of the preceding conditions, the modem automatically transitions back

into Idle Mode.

3.2.2. Transmit Mode

When the first byte of serial data is received from the UART in the DI buffer, the modem

attempts to shift to Transmit Mode and initiate an RF connection with other modems. After

transmission is complete, the modem returns to Idle Mode.

RF transmission begins after either of the following criteria is met:

1. RB bytes have been received in the DI buffer and are pending for RF transmission (refer to

RB (Packetization Threshold) command, p34).

The RB parameter may be set to any value between 1 and the RF packet size (PK), inclusive.

When RB = 0, the packetization threshold is ignored.

2. At least one character has been received in the DI buffer (pending for RF transmission) and

RO time has been observed on the UART (refer to RO (Packetization Timeout) command).

The timeout can be disabled by setting RO to zero. In this case, transmission will begin after

RB bytes have been received in the DI buffer.

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.

Note: RF reception must

complete before the

modem is able to enter

into Transmit Mode.