RS232 LOW COST RF MODEM
FM-232C-433
ERROR CHECKING / RELIABILITY
Several methods are employed,
a. Checksum.
b. I/D & COMMAND : bits are sent to on each packet.
c. Data Sequencer : this ensures that the receiving Modem knows the logical sequence of packets so that if
an ‘acknowledge’ only, was destroyed causing re-transmission of a data packed, the receiver knows this
packet has already been received and discards the data.
ANTENNA & RF MODEM POSITIONING
The helical antenna provided will provide adequate range for most applications. For optimum range, follow
these general rules:
·
·
·
The space around the antenna is as important as the antenna itself.
The optimum position is to locate the antenna so that is protrudes upwards.
If this is not possible due to other design constraints, try to keep the antenna away from other potential
sources of interference such as transformers, batteries and PCB tracks, especially ground planes.
Note: Personal computers are one of the one of the greatest generators of RF interference. Ensure the RF
Modem is situated as far away as possible.
CE COMPLIANCE
This product is a sensitive electronic instrument and as such it may temporarily be affected by Radio
Transmitting Devices being used in close proximity to it (such as Mobile Phones, Walkie Talkies, CB Radios,
Radio Model Controllers and some Microwave Ovens). If it does exhibit symptoms such as display of erratic or
erroneous data, try moving this product away from the source of interference or switching off that source of
interference whilst you are using this product.
CONNECTION INFORMATION
The RF Modem interfaces to the host computer via RS232 connection. A standard DB9 connector as shown in
the diagram below.
PC Serial Port
DTE
(DB25)
RF Modem
DCE
(DB9F)
PC Serial Port
DTE
RF Modem
DCE
(DB9F)
(DB9)
8
3
1
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
Tx
2
3
4
5
6
7
8
9
Tx
2
Rx
Rx
20
7
DTR
DTR
GND
GND
6
RTS
CTS
4
RTS
CTS
5
22
DS232_2
June 00
©2000 Reg. No. 227 4001, ENGLAND
Page 5
RFSOLUTIONS [ RFSOLUTIONS.LTD ]
