User's Manual

Data enters the 24XStream the DI pin as an asynchronous serial signal. The serial signal is idle

(high) when no data is being transmitted. Each data packet consists of a start bit (low), 8 data

bits, and a stop bit (high) as shown below in Figure 4.

The 24XStream modules transfer exactly 8-bits over the air. The start and stop bits from the

UART signal are not actually transmitted, but are regenerated on the receiving module before

they are sent out the serial port. This allows for the following data configurations to be sent:

• 8-bit, no parity, 1 stop bit

• 7-bit, even parity, 1 stop bit

• 7-bit, odd parity, 1 stop bit

• 7-bit, no parity, 2 stop bits

Since the 24XStream is half-duplex, it can only transmit or receive at a given time. Thus, once

the first byte is detected on the DI pin, the 24XStream immediately begins transmitting the

incoming data unless over-the-air data is already being received. In this case, the data on the DI

pin is stored in the data buffer until data is no longer being received at the antenna. If the

24XStream receives a lengthy sequence of data, the data buffer could reach its capacity (132

bytes) in which case the *CTS signal will need to be implemented (see *CTS section below).

Also, the 9600 and 19200-baud modules allow the incoming serial data to be transferred at a rate

of 2400-57600 bits/second. Serial data can be transferred to the module at a rate equal to or less

than the module’s over-the-air baud rate without any problems. However, if the serial interface

rate is set to exceed the module’s baud rate (9600 or 19200 bps respectively), *CTS must be

implemented since the data buffer may become full.

DO (Data Out) – Pin 3 (Output)

Data received from over-the-air transmissions is checked for errors and then sent to the DO pin.

____

CTS – Pin 1 (Output)

___

The CTS pin (clear to send) informs the host device whether or not serial data can be sent to the

24XStream module. When *CTS is low, serial data can be sent to the 24XStream module. All

incoming serial data is stored in a data buffer until the next data packet is transmitted (over-the-

air). The data buffer can hold up to 132 bytes of data. Once the data buffer contains 115 bytes,

the 24XStream module drives the *CTS signal high (de-asserts it) to alert the host device to stop

sending serial data. *CTS remains high until less than 98 bytes are in the buffer.