LK1

Eval RPC has two modes of operation:
1) Normal mode (Jumper removed)
2) Diagnostic mode (Jumper inserted)

In normal mode, the Eval-RPC behaves similarly to a Radio Packet Controller (RPC). The board can be used in conjunction with a host microcontroller or PC to transmit & receive packetised data.
Diagnostic mode can be used to evaluate system performance in the intended environment.

LK2

This link connects the appropriate crystal to the Eval-RPC oscillator circuit for data bit rate selection.

Crystal Frequency

All timings within the Eval RPC (except sleep) are determined by the clock frequency. The standard frequencies are 2.4576MHz and 16.384MHz.

         
Figure 1: Jumper selection for data rate

When the Jumper is placed as shown on the above left diagram, 2.4576MHz, the Eval RPC will transmit data at 9.6kbps.

LK3

The module TXD line is normally driven directly with data from the Eval-RPC chip. However, it can also be driven from an external digital or analogue source if required. In this case, removing LK3 allows the TXD line to be disconnected from the internal Eval-RPC data for correct operation.

LK4

The TX2, HX1, BiM and BiM2 operate on 5V supply and hence their TXD input can be in 0-5V range. However, TX1, NTX2, TX3A, BiM1 and BiM3A operate internally on 3V supply and their data input should be in 0-3V range.

This LK4 jumper link grounds the R4, making a parallel connection to the TXD input.
Very high input impedance of TXD with R4 resistor in parallel combination will give effective impedance equivalent to R4 (3.3k) resistor. R3 (2.2k) and R4 (3.3k) will form a potential divider reducing the logic level from 0-5V to 0-3V range. LK5 jumper should be removed while LK4 jumper link is inserted

LK5

Removing the LK4 jumper and linking the LK5 returns the Eval-RPC drive amplitude of module TXD back to 0-5V

LK6

The RX2 and BiM/BiM2 modules have Carrier Detect (CD) output instead of RSSI output featured on RX1, RX2A, NRX2, RX3A, BiM1 and BiM3A modules. Inserting the LK6 will enable the CD LED to work with RX2 and BiM/BiM2 modules. It should be removed when evaluating modules with RSSI output and CD LED output should also be ignored.

Diagnostic Modes

To enter the DEBUG mode, Jumper Link (LK1) (below the 9V battery) should be connected across TXR and 0V pin. The RESET button should be pressed while the Jumper Link is connected across TXR and 0V.

Note: All the Oscilloscope screen capture and Spectrum Analyser screen capture given on the manual are instantaneous and they will vary with time.

Mode 0 - Preamble Detector

Applies to Evaluation Kit with Receiver:

Insert Receiver module in one of the Evaluation Kit and Transmitter module on another.
Transmitting and Receiving unit should operate at same data rate. i.e. LK2 position on both evaluation kit should be same position on both evaluation kits.
If the jumper LK2 is at position A, the preamble will be a 4.8kHz or 9.6kbps square wave signal.

In this mode, receiver is continuously powered up (RX LED on) and if preamble, 32kHz or 64kbps square wave signal, with jumper LK2 at position F, is detected the SIGNAL line is pulled low lighting the SIGNAL LED. RXR will also be pulled low lighting the OK LED to indicate that valid preamble was received.

An Evaluation Kit with Transmitter is powered on (TX LED on) continuously (Mode 2) to transmit preamble. The TX line is held low (blue TX waveform) by the Eval-RPC and it feeds 32kHz square wave signal into TXD pin (green TXD waveform) of the Transmitter. Oscilloscope is triggered on TXD.

Other Evaluation Kit with receiver is also powered on (green RX LED on) continuously (Mode 0). AF output (red AF waveform) and RXD output (brown RXD waveform) are monitored.

The AF output is at 1.16V DC with about 240mV AC sine wave, which is digitised by the Adaptive Data Slicer in the Receiver to re-produce the received preamble. (Ground level of AF is at the bottom of the screen)

Note: LK3 should be removed when connecting analogue I/O board.

Mode 1 - Pulsed Receiver

Applies to Evaluation Kit with Receiver:

Receiver is switched on for about 7ms and Eval RPC checks for preamble. If preamble is detected the SIGNAL line is pulled low. This will light up the SIGNAL LED. If not, the Receiver is turned off for about 10ms and the process is repeated. OK LED will also light up if a valid Preamble is detected.

Figure 3: receiver power up to valid data timing measurement

Applies to Evaluation Kit with Transmitter:

Transmitter is turned on continuously and preamble is transmitted. This complement mode can be used with Mode 0 as a pair.

Figure 4: Transmitter spectrum with 32kHz (64kbps) square wave modulation

The above frequency spectrum shows a Carrier Frequency in the middle and FM side bands on both sides. Each side band is spaced 32kHz apart. This mode can also be used to measure modulation bandwidth at maximum data rate.

Note: Mode 2, with LK3 removed, can be also be used as TX On mode to switch on the transmitter, when feeding analogue signal or external data. LK3 should also be removed when analogue I/O board is connected.

RF Carrier will not be modulated by the data from Eval RPC if the LK3 is removed. The spectrum of unmodulated carrier with TXD held at 0V is given below

Figure 7: Unmodulated transmitter spectrum when TXD is at 0V

It can be used to check the phase noise of the transmitter.

Mode 4 - Transmit Random Code

Applies to Evaluation Kit with Transmitter:

Transmitter is turned on and the carrier is modulated by a 8 bit maximal length (255) pseudo-random code at 15.6ms per bit (at 64kbps). On the receiving end, the data output RXD line can be connected to an Oscilloscope to obtain an eye diagram.

Figure 8: Transmitted and received pseudo-random code

Eye Diagram:

An eye diagram is an oscilloscope display in which a pseudo-random digital data signal from AF output of a receiver is repetitively sampled and applied to the vertical input, while the data rate (RXR) on the transmitting unit is used to trigger the horizontal sweep. The picture one obtains is a superposition of ones and zeros output.

Figure 9: eye diagram of receiver

System performance information can be derived by analyzing the display. The horizontal width of the lines gives the jitter (phase noise) and the rise and fall times of the data pulses can be measured from the "crossings". An open eye pattern corresponds to minimal signal distortion. Distortion of the signal waveform due to intersymbol interference and noise appears as closure of the eye pattern.

Applies to Evaluation Kit with Transmitter:

The transmitter is turned on for about 8ms and normal preamble (length used for normal data transmission) is sent. Then transmitter is turned off and waits for equal amount of time before another cycle.

Figure 11: TX spectrum when transmitter is pulsed to transmit preamble

Figure 12: pulsed preamble transmission and received preamble

This mode can be used to test the power up time of transmitter and settling time of the receiver module when receiver is already powered up.

Mode 6 - Echo

Applies to Evaluation Kit with Receiver (and Transmitter):

Receiver is turned on. Checks for preamble and if it finds a preamble, then it locks on to the data and receives the data packet. SIGNAL LED will be turned on if the preamble is detected.
Then error check is carried out on the received data and if it passes, the OK LED is turned on and waits for a Transmit to Receive Change Over Delay period. Then it retransmits (echoes back) the packet to the transmitter.

Figure 13: Receiver unit echoing back to transmitting unit on every valid packet

The above oscilloscope screen capture shows RXR line pulled Low every time valid packet is received. Same RXR line activates the OK LED.

In the oscilloscope screen capture below, the receiving (mode 6) unit's echo did not reach the transmitting (mode 7) unit. Therefore, transmitting moves onto transmitting next packet after waiting for the time required to detect preamble of the echo packet.

Note: This may also happen if the Transmitter is removed from the receiving (mode 6) unit.

Figure 14: Transmitting unit moves to next transmission because echo was not received

Mode 7 - Radar

Applies to Evaluation Kit with Transmitter (and receiver):

Transmitter is turned on and sends a packet with Universal Eval Kit XX as data where XX will be a Packet Counter from 00 to 63. Then transmitter is turned off and receiver is turned on for 8ms. Checks for preamble and if it finds a preamble, then it locks on to the data and receives the packet. Then error check is carried out and if it passes, OK LED will be lit.

Nevertheless, it will continue the above process but the packet counter value will be increased with each transmission.

This mode can be used along with Mode 6 (Echo Mode) to function as a 'Pin-Pong' system. This provides a very effective method for Range Testing and Antenna Type Evaluation.

If one eval kit is set to Mode 6, then other eval kit can be set to Mode 7. By walking around the site where the final product based on the Radiometrix Modules are going to be used, the range and antenna type requirements, interference, etc could identified well in advance. The OK LED will be ON as long as the 'Ping-Pong' the units are within the radio range and the wireless link is error free.

OK LED will start to flicker on the Eval Kit set to mode 7, if some of the echoed packets are received with bit errors.

Note: Operating range of the modules will apper to be shorter due to the RF power loss in the common 50W microstrip.

Figure 15: Receiver unit sampling (RXD output) received data bit but echo was received

Figure 16: TX spectrum when transmitting radar mode ASCII data packet

Mode 8 - Local Loop Test

Applies to Evaluation Kit with both Transmitter and Receiver:

This Eval RPC puts the transceiver or transmitter & receiver pair on same Eval kit into a local loop back (both TX & RX on), a test code is continuously sent and recovered. The SIGNAL LED will light to indicate a pass.

Figure 17: TX spectrum when transmitting unbalanced test code

Figure 18: Transmitted and received unbalanced test code

Figure 19: expanded view of the unbalanced test code

The above waveform shows the test pattern used to evaluate receiver and its Adaptive Data Slicer.

Jumper Link (LK1) (below the 9V battery) should be removed and the RESET button should be depressed.

This will effectively put the Eval RPC into normal (non-diagnostic) mode. Therefore, any interface cable with Host Microcontroller or Parallel Port of a PC can be interfaced with the Eval Kit.

Figure 20: Transmitted and received 27-byte (full length) data packet

PC Interface

Parallel Port Interface Adaptor can be used to interface the Universal Evaluation Kit to Parallel port using standard D25 parallel port extension cable (One to One connection with D25 plug connector on one end and D25 socket on other end)

RPC Development Kit software can be used to view/modify the RPC EEPROM values. Data transmission can also be monitored using the same software.
This feature will help debug the host software routines in the design & development stage of a product.

Figure 22: RPC Dev-Kit software showing the default EEPROM values of Eval RPC

Note: RPC development kit software runs on the MS-DOS operating system or Windows 95/98/98SE/ME. It will not run under NT4.0/XP/2000

Figure 23: Eval RPC to Parallel port interface

Even though the Radiometrix modules are specifically designed for data transmission, they can also be used for analogue transmission excluding signals which contain DC level or very low frequency components.

Analogue I/O board should be connected to the 10-pin header (J12) on top right hand corner of the Evaluation Kit. Jumper link on LK3 should also be removed to disconnect the TXD line from Eval RPC's data pin.

Analogue I/O contains:
1) Analogue transmit signal amplifier
2) Buffered audio output for stereo headphone/speaker.

DC component in the analogue signal is removed via capacitor. A simple common emitter amplifier with negative feedback is used to amplify the small AC signal from few mV to few Volts. Signal level on TXD pin should be large enough to cause enough FM deviation on the RF carrier of the transmitter. Otherwise, the small demodulated AF output, under poor signal to noise ratio (S/N) conditions, will be indistinguishable or submerged in the noise. The AC signal is also biased at 1.25V, so that it is at half the transmit data voltage swing of 0-3V.

User can feed a function/waveform generator output through the Analogue In and receive the analogue output on the other kit to evaluate the performance of the module under various signal frequencies and amplitudes.

Note: a large signal on the Analogue input will saturate the amplifier and clipping may occur on the amplified signal.

Audio Frequency (AF) output can be monitored with an headphone or speaker to identify any noise or interference source in the environment. It can also be connected to Line In of a PC. User can walk around the building or field with the receiving kit while constantly listening to the Analogue Out. A crackling sound can be heard whenever user passes through a null spot or poor reception area. Any interference source can be clearly distinguished from expected analogue sound.

Warning: Headphone should be worn after switching on the transmitting kit and it should only be worn while the transmitter is on. It should be removed before switching off the transmitter. The output on the headphone will be too loud if the transmitter is switched off.

AF output will contain noise if the RF signal level drops. The unmuted noise level on the AF output has significantly higher amplitude compared to data signal level.

Figure 24: Analogue I/O board circuit diagram

Figure 25: Evaluation of TX2 & RX2 using Universal Evaluation Kit

Figure 26: Evaluation of TX3A & RX3A using Universal Evaluation Kit

Figure 27: Evaluation of BiM or BiM2 using Universal Evaluation Kit

Figure 28: Evaluation of BiM1 & BiM3A using Universal Evaluation Kit