TRM-915-R250 datasheet(9/39 Pages) LINX

9 / 39 page

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Reset to Factory Default

It may be necessary to reset the non-volatile registers to their factory

defaults. To reset the module, hold the CMD line low and cycle power to

hardware-reset the module. The CMD line must remain low for a minimum

of 600ms after resetting the module. Once the CMD line is released, the

module’s non-volatile registers are reset to factory defaults.

Compatibility Mode

The 250 Series modules support a mode that allows them to communicate

with the smaller, lower power 25 Series modules. The 250 Series operates

at a much narrower receive bandwidth (200kHz) than the 25 Series

(600kHz). To allow interoperability, the 250 and 25 Series transceivers

support a compatibility mode that allows the modules to communicate

effectively with each other.

Compatibility mode reduces the maximum RF data rate to 76.8kbps. All

UART baud rates are supported, although the RF data rates associated

with baud rates 31,250; 38,400; 57,600 and 115,200 are reduced.

Automatic Gain Control and Manual Gain Control

The gain setting of the receiver’s low noise amplifier (LNA) is adjustable.

By default, the 250 Series is factory-configured to use its internal automatic

gain control (AGC) circuit to manage receiver sensitivity. Reducing the gain

increases the linearity of the receiver, but reduces maximum sensitivity;

increasing the gain does the opposite. Generally speaking, higher

linearity (increased third order input intercept point, IIP3) gives improved

performance in high-interference environments; high gain yields better

performance in low-interference environments.

The module contains an AGC circuit that manages these settings

automatically, and it should be used whenever possible. However, when

attempting to make analog RSSI measurements, fixing the LNA gain

produces more meaningful results. Digital RSSI readings are internally

compensated and may be taken with AGC enabled.

Exception Engine

The modules are equipped with an internal exception engine. If errors occur

during module operation, an exception is raised. Exception codes are

stored in the regEXCEPTION register and are cleared once they are read.

If an exception code is already present in regEXCEPTION when an error

occurs, the new exception code overwrites the old value.

Exception Codes

Exception codes are organized by type for ease of masking. Figure 9 lists

the exception codes and their meanings. All other values are reserved.

Exception Masking

The EX line can be asserted to indicate to the host that an error has

occurred. The exception mask provides a simple method of choosing

which errors cause the line to toggle. If the result of ANDing the exception

code with the exception mask is non-zero, the EX line is asserted. The

regEXCEPTION register must be read to reset the line. Figure 10 lists some

example exception masks.

The exception mask has no effect on the exceptions stored in the

exception register. It only controls which exceptions affect the EX line.

250 Series Transceiver Exception Codes

Exception Code

Exception Name

Description

0x08

EX_BUFOVFL

Internal UART buffers overflowed.

0x09

EX_RFOVFL

Internal RF packet buffer overflowed.

0x13

EX_WRITEREGFAILED Attempted write to register failed.

0x20

EX_NORFACK

Acknowledgement packet not received

after maximum number of retries.

0x40

EX_BADCRC

Bad CRC detected on incoming packet.

0x42

EX_BADHEADER

Bad CRC detected in packet header.

0x43

EX_BADSEQID

Sequence ID was incorrect in ACK packet.

0x44

EX_BADFRAMETYPE

Unsupported frame type specified.

Figure 9: 250 Series Transceiver Exception Codes

250 Series Transceiver Example Exception Masks

Exception Mask

Exception Name

0x08

Allows only EX_BUFOVFL and EX_RFOVFL to trigger the EX line

0x10

Allows only EX_WRITEREGFAILED to trigger the EX line

0x20

Allows only EX_NORFACK to trigger the EX line

0x40

Allows only EX_BADCRC, EX_BADHEADER, EX_BADSEQID and

EX_BADFRAMETYPE exceptions to trigger the EX line

0x60

Allows EX_BADCRC, EX_BADHEADER, EX_BADSEQID, EX_

BADFRAMETYPE and EX_NORFACK exceptions to trigger the EX

line

0xFF

Allows all exceptions to trigger the EX line

Figure 10: 250 Series Transceiver Example Exception Masks

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