9XTend™
OEM
RF
Module
–
Product
Manual
v1.2.4
©
2005
MaxStream,
Inc.
Confidential
&
Proprietary
13
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 module computes the CRC on all incoming RF data. Received data
that has an invalid CRC is discarded [See Receive Mode section, next page].
2.2.3.
Receive Mode
If a module detects RF data while operating in Idle Mode, the module transitions into Receive
Mode to start receiving RF packets. Once a packet is received, the module checks the CRC (cyclic
redundancy check) to ensure that the data was transmitted without error. If the CRC data bits on
the incoming packet are invalid, the packet is discarded. If the CRC is valid, the packet proceeds
to the DO Buffer.
Figure
2.8.
Receive
Mode
Data
Flow
*
Refer
to
the
Addressing
Options
[p37]
section
of
the
RF
Communication
Options
section
for
more
information
about
address
recognition.
The module returns to Idle Mode when valid
RF data is no longer detected or after an
error is detected in the received RF data. If
serial data is stored in the DI buffer while
the module is in Receive Mode, the serial
data will be transmitted after the module is
finished receiving data and returns to Idle
Mode.
2.2.4.
Shutdown Mode
Hardware Sleep
For applications where power consumption must be kept to a minimum during idle periods,
Shutdown Mode offers the lowest power mode available to the module.
When the
pin (pin 7) is driven low, the module is forced into shutdown mode. Any
communication in progress (transmit or receive) will be halted and any buffered data will be lost.
For any other mode of operation,
must be driven or pulled high. While in shutdown mode,
the module’s VCC pin draws less than 1 µA.
Immediately after the
pin changes state from low to high, the module resets. After reset,
there is a delay that must be observed. See reset section for the delay time.
While
pin is driven low, the following pins are set to high impedance by the module: DCD,
TX_PWR, RX LED, DO and
(See pin signal descriptions, p6). The
line (also used for
RSSI indication) is driven low during shutdown.
The following input pins may continue to be driven by external circuitry when in shutdown mode:
PIN_PWR_DWN,
, DI and
.
Note: Because the DO pin also goes high impedance, if the XTend Module is connected to a
processor, the UART receive pin could be floating. A weak pull-up should be placed between the
module and the microcontroller so that data isn’t interpreted as being transmitted to the
microprocessor.
