EW
N
Issue 1, 27 April 2007
Radiometrix
Hartcran House, 231 Kenton Lane, Harrow, HA3 8RP, England
Tel: +44 (0) 20 8909 9595, Fax: +44 (0) 20 8909 2233
RPM1
VHF Radio Packet Modem
The VHF Radio Packet Modem (RPM1) is a low cost intelligent radio packet modem
that enables a two way radio network/link to be simply implemented between a
number of digital devices. The RPM1 uses addressable data packets with error
checking, packet acknowledgements and retransmissions to achieve a reliable
transparent wireless data link. Built for ease of use and rapid installation, the serial
interface ensures direct connection to microprocessors or to RS232 port via RS232
driver while remote configuration enables post installation setup of the modem.
Features
point-to-
Addressable point-to-point
Point-to-
Point-to-Multipoint and broadcast modes
Inverted RS232 interface at 5V or 3.3VCMOS level
600-
DTE speed 600-115200bps
with
Overall throughput: 3.7kbps with ACK
5.3kbps without ACK
Single 5V or 3.3V (10mW max) supply
Flow control – Hardware (CTS), None
Usable range over 1km
Built-
Built-in command line configuration
Built-
Built-in RF link diagnostics
over-
Remote over-air unit configuration
current,
Low operating current, Auto standby mode
220-
489-
Conforms to European ETSI EN 300 220-3 and EN 301 489-3 (at 10mW)
Conforms to Australian/New Zealand AS/NZS 4268:2003 (at 100mW)
Dimensions: 39mm X 23mm X 15mm
Available as RPM1T transmitter and RPM1R receiver for one way communication
communication
Figure 1: RPM1-173.250-3
Applications
GPS (NMEA) position reporting
Telemetry and telecontrol
EPOS equipment, barcode scanners, belt clip printers, stock control, job allocation
Remote data acquisition system, data loggers
In-
In-building, environmental monitoring and control systems
monitoring
High-
High-end security and alarm signalling
Automated Monitoring and Control Systems
Fleet management, vehicle data acquisition
Radiometrix Ltd.
VHF Narrow Band FM Radio Packet Modem
page 1
I
NTRODUCTION
The
RPM1
is a self-contained Radio Packet Modem module that requires only a simple antenna, 5V
supply and a serial I/O port on a host microcontroller or PC.
The module provides all the RF circuits and processor intensive low level packet formatting and packet
recovery functions required to inter-connect any number of devices with serial port in a radio network.
A continuous stream of serial data downloaded by a Host microcontroller into the
RPM1
serial receive
buffer is transmitted by the
RPM1’
S
transceiver and will "appear" in the serial buffer of the addressed
RPM1
within radio range.
Figure 2: Point to point wireless link with RPM1 + Host microcontroller
1. F
UNCTIONAL
D
ESCRIPTION
The RPM1 is a connection oriented modem module for sending and receiving serial data via an RF
communications link.
The RPM1 handles all necessary protocol related functions of validation and retries to ensure error free
and uninterrupted data is sent over the communications link. All data transfers between a pair of RPM
S
are fully acknowledged, thus preventing the loss of data. Bit coding and checksums are used on the data
packets to ensure the validity of the received data at the remote end.
Figure 3: RPM1 block diagram
Radiometrix Ltd.
VHF Narrow Band FM Radio Packet Modem
page 2
1.1 O
PERATING STATES
The R
ADIO
P
ACKET
M
ODEM
has three normal operating states:
•
S
HUTDOWN
•
S
TANDBY
•
C
ONNECTED
S
HUTDOWN
The
S
HUTDOWN
state is entered by asserting the WAKE/DTR input pin high (Vcc). It effectively
forces the RPM1 into a suspended state. Communications cannot be made with the RPM1 in this
state. WAKE/DTR pin should be pulled Low by host or connected to 0V to Enable the RPM1.
S
TANDBY
Immediately after power up and during normal operation, the RPM1 will automatically enter
standby mode where it is waiting for a connection request from a remote RPM1 module.
While in this mode a remote connection request can be received which will place the RPM1 into a
connected state allowing it to then start receiving data from the remote unit. The connected host
device can also send data to the RPM1 via the serial interface which will force the module to send
a connection request to the remote RPM1 module, thus effectively setting up a logical connection
between two units and allowing data to be transferred.
C
ONNECTED
On receipt of a connection request from a remote unit, the RPM1 immediately enters a connected
state. This effectively allows the RPM1 modems to start sending and receiving data.
In-coming data is sent to the host via the serial port in the same form as it was given to the
remote RPM1 module.
Figure 4: RPM1 transmitting data at 5.3kbps during ZMODEM file transfer to a remote RPM1
Radiometrix Ltd.
VHF Narrow Band FM Radio Packet Modem
page 3
2 The Host Interface
2.1 S
IGNALS
The connection to the RPM is a full duplex serial interface supporting baud rates from 600bps to
115200bps. Additional control signals are provided to assist in flow control, configuration and power
saving in the RPM1.
Figure 5: Physical dimensions and pinouts
Pin name
RF GND
RF
RXSELCT
TX SELECT
TXD/AF
Pin
1, 3
2
4
5
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
6, 22
Pin Function
RF signal ground
RF signal
Receiver Select
Transmitter Select
Transmitted Data
or demodulated signal
FRPC Data line
FRPC Data line
Preamble Detect
FRPC reset
Receive Acknowledge
Receive Request
Reset
Enter Setup
Wake or Shutdown
Serial transmitted data
Serial Received data
Clear To Send
Force 9600bps
Vcc Supply
Ground
In/Out
Input or Output
Input
or Output
Input
or Output
Input
or Output
NC
NC
Output
NC
NC
Output
Input
Input
Input
Input
Output
Output
Input
Input
-
Description
BNC casing/coax braid connection
Antenna pin/coax core connection
Internal RF Receiver Enable to BiM1
or RF Receiver Active Indicator
Internal RF Transmitter Enable to BiM1
or RF Transmitter Active Indicator
Transmitted Packetised Data to BiM1
Analogue Demodulated signal from BiM1
Internal data line between RPM and FRPC
Internal data line between RPM and FRPC
Valid preamble indicator
Resets FRPC which also isolates BiM1
RPM to FRPC download Request Acknowledge
Valid Data packet indicator
Hardware reset of the RPM1
Enter RPM1 configurator after a RESET
Wakes RPM1 when low, shuts down when high
Host (DTE) to RPM1 serial transmit data
RPM1 to host (DTE) serial received data
Hardware flow control of data from host (DTE)
Force the RPM1 serial interface to 9600bps
+5VDC or +3.3VDC
Supply Ground internally connected to RF GND
D3
D2
SIGNAL
RST
RXA
RXR
RESET
SETUP
WAKE/DTR
TXD
RXD
CTS
DEFAULT
VCC
GND
notes:
1. RXD/TXD lines are true data
2. Active low SETUP, DEFAULT inputs r
equire external 10kΩ pull-up to VCC.
3. Logic levels are 5V CMOS unless 3.3V variant is used.
4. WAKE pin should be pulled to ground if DTE cannot provide DTR signal
5. TXSELECT, RXSELECT, SIGNAL, RXR, CTS can be connected to LEDs via 1k
Ω
series resistors
2.2 R
ADIO
P
ACKET
M
ODEM
R
ESET
R
ESET
The Reset signal is internally pulled up to Vcc via a 10kΩ resistor. A reset aborts any transfers in
progress and restarts the RPM1.
H
OST DRIVEN RESET
Minimum low time: 1.0
µs,
after reset is released (returned high). The host should allow a delay
1ms after reset for the RPM1 to initialise itself.
Radiometrix Ltd.
VHF Narrow Band FM Radio Packet Modem
page 4
2.3 H
OST
T
O
R
ADIO
P
ACKET
M
ODE
D
ATA
T
RANSFER
Data is transferred between the RPM1 and the H
OST
using an asynchronous serial protocol. The default
protocol settings are 8 data bits, no parity and 1 stop bit (8n1). The baud rate setting for the serial
interface is user settable from 600bps to 115200bps.
TXD
Data from the connected host (DTE) is received by the RPM1 through
TXD
pin.
CTS
A single handshake line,
CTS,
controls the flow of data into the RPM1. The serial receive buffer of
the RPM1 is 96 bytes deep. The
CTS
will be asserted High (VCC) by the RPM1 when the receive
buffer hits approximately 66% full. It is advisable to limit the number of characters sent to the
RPM1 after the
CTS
control line is asserted. This will help to reduce the possibility of lost data
due to internal buffer overruns in the RPM1. The RPM1 will clear the
CTS
when the internal
serial receive buffer falls below 33% full.
RXD
Upon the RPM1 receiving data from a remote unit, the received data is sent to the connected host
(DTE) device through the
RXD
pin.
2.4 E
NTERING
R
ADIO
P
ACKET
M
ODEM
C
ONFIGURATOR
Configuring the RPM1 is accomplished by using a built-in command line configurator. The configurator
is entered by asserting the
S
ETUP
input of the RPM1 while resetting the RPM1.
S
ETUP
Holding
S
ETUP
low during a reset cycle will force the modem into the configurator. The state of
this input is checked while the RPM1 starts up from either power on or reset.
H
OST DRIVEN
S
ETUP
The Setup pin may either be driven by the host (recommended) to enable host controlled
configuration of the RPM1 or pulled up to V
CC
via a suitable pull-up resistor (10kΩ).
2.5 F
ORCING
D
EFAULT
S
ERIAL
B
AUD
R
ATE
Asserting this pin low forces the RPM1 to start-up with a default baud rate of 9600bps, 8 data bits, one
stop and no parity.
D
EFAULT
During a
R
ESET
the
H
OST
must hold
D
EFAULT
low to force the RPM1 serial interface to default to
9600bps. This is ideal if the serial baud rate has been forgotten or incorrectly set.
H
OST DRIVEN
D
EFAULT
The
D
EFAULT
pin may either be driven by the host (recommended) or pulled up to V
CC
via a
suitable pull-up resistor (10kΩ).
2.6 F
ORCING
R
ADIO
P
ACKET
M
ODEM INTO SLEEP MODE
Asserting the
WAKE
input high forces the modem into a low power sleep mode. This effectively shuts
down the RPM1 and prevents it from sending or receiving any data. It is a method for conserving power
when the modem is not required.
D
TR
During normal operation
WAKE
pin can be pulled high to force the RPM1 to shutdown into low
power sleep mode.
H
OST DRIVEN WAKE
The
WAKE
pin may either be driven by the host (recommended) or pulled Low to 0V.
WAKE
/
Radiometrix Ltd.
VHF Narrow Band FM Radio Packet Modem
page 5
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