RFD21733 Datasheet, PDF (34/76 Pages) List of Unclassifed Manufacturers – Compliance Approved 2.4 GHz RF Transceiver Modules with Built-In RFDP8 Application Protocol

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7/10/2011 1:40 AM
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RFDP8
RF Module
RFD21733
RFD21735
RFD21737
RFD21738
RFD21739
RFDP8
RFDANT
RFD21742
RFD21743
RFD21772
RFD21773
KEYFOBs
anything other then a solid logic level on the TXD pin. Note you can also pull it to ground using a 47k resistor to
terminate it if you require, but most applications will want to terminate by a pull up resistor if the pin is unused.
The Eval boards pull it to ground using a 47K resistor, because the Eval boards are setup to work in 8 different
modes, if you are just using UART only, you will want to pull it high rather then low.
There is a general purpose IO line in mode 2 and mode 3 which is called LOGIC IO. This is a powerful feature
which allows you to not only send serial data back and forth using the TXD and RXD, but in addition you can
apply a high logic level to the LOGIC IO pin and it will start transmitting without the need for sending serial data
into the TXD pin. Once it is transmitting, any mode 2 or mode 3 receiver's LOGIC IO pin will go high for the same
duration of time. This allows you to send switch data between two transceivers as well as serial data. In some
applications this is very useful since you can use this feature to have one master device turn on a slave device
and wait for the slave device to be ready to communicate using the UART and then begin sending data to it rather
than keeping it awake all the time.
Bi-Directional LOGIC IO Operation – In Mode 2 and Mode 3.
UART mode includes an additional bi-directional general-purpose IO line. The IO signal is generally an input, and
should be pulled to GND with an appropriately sized resistor (for example 10k). If the IO signal is driven high, the
module will transmit this information, and any UART which receives the data will turn its IO signal into an output
and drive it high. This will continue until 20ms pass without receiving any new data, or until the module receives a
packet which indicates that the IO signal should be driven low and turned back to an input. The state of the IO
signal does not require any extra data in the radio stream, and so is “free” in the packet overhead.
When the module is driving its IO signal high, it will periodically change the pin to an input and check to see if it
remains high, before changing it back to an output. This causes a periodic dip in the signal, 1ms every 12-16ms,
and so any circuitry which relies on a steady-state output from the IO signal should include conditioning (for
example a retriggerable one-shot with a hold time of 2ms) to avoid adverse effects.
Note even if there is no data inputted into the TXD line and the TXD line is pulled high or low through a resistor
and kept at a steady state, simply applying a high on the LOGIC IO pin will cause that radio to start transmitting
and stay transmitting as long as the LOGIC IO pin is kept high. This is a huge advantage if you want to use it to
reset a remote device for example or use it to turn on an external device located at the receiving radio, all without
the need of doing decoding of data on the receiving end to process the command signal.
Also another very powerful feature of this function is to use it to pass command signals to the receiving radio
without needing to use escape codes hidden within the data stream which can always cause problems, this
LOGIC IO feature with the RFDP8 protocol completely resolves this long time industry problem with UART
escape codes with wireless devices.
IMPORTANT NOTE – LOGIC IO Pin (This pin is BI-DIRECTIONAL)
The LOGIC IO pin MUST be terminated when in mode 2 or 3, (pulled to ground with a 47k resistor) or it will float
and cause the transmitter unintentionally. All inputs must be terminated properly and this one is no exception. If
you do not plan on using it, tie it to ground using any resistor between 10k to 47k. Note this is a BI-
DIRECTIONAL pin so do not directly connect to an output or to ground, you must use a pull down resistor. Also,
when in use with a microcontroller pin you should consider using a series 1k resistor as well between the LOGIC
IO pin and your controller pin since that will prevent any possible conflicts that might happen if you chose to drive
the pin when it was an output by mistake, which can be a very common occurrence. In addition, if you plan on
connecting the LOGIC-IO Pin to a pushbutton switch, then you must have a series current limiting resistor in the
order of about 1k, so when you press the button and drive the pin high, you can never have more then about a
1mA load on the pin just in case it happened to turn into an output at anytime since it is bi-directional. Of course,
the 47k pull down would still be required as well to make sure the input is not floating.
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