Radiometrix Ltd, SpacePort Modem

page 5

The connection to the SPM 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 SPM. Figure 3 shows an overview of the interface signals to the SPM.

Pin name

Pin

Pin Function

In/Out

Description

RF GND

1, 3

RF signal ground

BNC casing/coax braid connection

RF

2

RF signal

Input or Output

Antenna pin/coax core connection

RXSELCT

4

Receiver Select

Input

or Output

Manual RF Receiver Enable

or RF Receiver Active Indicator

TX SELECT

5

Transmitter Select

Input

or Output

Manual RF Transmitter Enable

or RF Transmitter Active Indicator

TXD/AF

7

Transmitted Data

or demodulated signal

Input

or Output

Transmitted Packetised Data to BiM2

Analogue Demodulated signal from BiM2

D3

8

SP2 Data line

NC

Internal data line between RPM and FRPC

D2

9

SP2 Data line

NC

Internal data line between RPM and FRPC

SIGNAL

10

Preamble Detect

Output

Valid preamble indicator

RST

11

FRPC reset

NC

Resets FRPC which also isolates BiM2

RXA

12

Receive Acknowledge

NC

Host to FRPC download request acknowledge

RXR

13

Receive Request

Output

Valid Data packet indicator

RESET

14

Reset

Input

Hardware reset of the SPM

SETUP

15

Enter Setup

Input

Enter SPM configurator after a reset

WAKE/DTR

16

Wake or Shutdown

Input

Wakes SPM when low, shuts down when high

TXD

17

Serial transmitted data

Input

Host (DTE) to SPM serial data

RXD

18

Serial Received data

Output

SPM to host (DTE) serial data

CTS

19

Flow control

Output

SPM to Host (DTE) flow control

DEFAULT

20

Force 9600bps

Input

Force the SPM serial interface to 9600bps

VCC

21

Vcc Supply

Input

+5VDC

GND

6, 22

Ground

-

Ground internally connected to RF GND

notes: 1. RXD/TXD lines are true data

2. The 4 input control lines are active low

3. Logic levels are 5V CMOS. See electrical specifications

4. Input control pins must be terminated, as pull-ups are not provided

5 Indicator outputs are active low which can be connected to LEDs

The Reset signal may either be driven by the host (recommended) or pulled up to Vcc via a

suitable resistor (10k

Ω). A reset aborts any transfers in progress and restarts the SPM.

Minimum low time: 1.0

µs, after reset is released (returned high). The host should allow a delay

1ms after reset for the SPM to initialise itself.

TX Select

Fast

Radio

Packet

Controller

(FRPC)

BiM2

UHF

Transceiver

SPACEPORT MODEM

RX Select

TXD

RXD

RESET

DEFAULT

SETUP

CTS/DSR

TXD

RXD

Radio

Packet

Modem

(RPM)

Host

D0

D1

D2

D3

TXA

RXR

RXA

RST

TXR

SIGNAL

WAKE/DTR

Figure 3: Host to SPM connection