User's Manual

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RF Digital Corp.
9/2/2010 12:02 PM
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RFDP8
RFDANT
RFD21743
Eval Board
RFD21773
Byte Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
1 Input 3 Input 2 Input 1/
RFID
RFID
2 ESN Byte 1
3 ESN Byte 2
4 ESN Byte 3
5 ESN Byte 4
In the first byte, bits 6 through 4 carry the state of the logic inputs, with a ‘1’ indicating the logic input on the
transmitter is high, and a ‘0’ indicating it is low. An RFID Transmitter will set both bits 0 and 4 to indicate that it is
a periodic transmission from an RFID Transmitter, and is set to ‘1’ if this is the case.
For example, if an RFID Transmitter with ESN 314CE686 sent a packet on its 2-second interval, a UART would
receive the bytes 11 31 4C E6 86 in binary format.
If input #1 on that same RFID transmitter were pulled high, the UART would receive the bytes 10 31 4C E6 86 in
binary format; since bit 0 is clear, the receiver can tell that this was not a periodic transmission.
Most ESN’s will contain at least one unprintable character, and so this data will not be suitable for displaying
directly in a terminal package (such as HyperTerminal), but a PC-based program or an embedded system (such
as the BASIC Stamp) can collect the data and display it in a more friendly fashion.
The ESN which the UART receives is the same one that is in the packet header. If the UART is in Network Mode,
and has not learned the ESN, it will never receive the packet, and there will be no output on the serial port.
UART to Logic Receiver
A UART can also send data to a logic receiver, which will decode the data and assert its outputs as though it
received a packet from a logic transmitter. The data format is very similar to the one described in the previous
section. The differences matter only when the receiver is in Network Mode.
The UART must follow a packet with at least 15ms of no data so that all bytes as described below are sent as a
single packet.
Note that a UART can send a single zero byte – all bits clear – to force a receiver to turn off its outputs
immediately, regardless of hang time.
Format 1:
Byte Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
1 Output 3 Output 2 Output 1
When the receiver is not in Network Mode, the receiver will accept any packet it receives, and so this is the
preferred format.
A receiver in Network Mode will use the UART’s ESN from the packet header to determine if it should accept the
packet. This allows one UART to send the same data to multiple receivers, provided that each receiver has
learned the UART’s ESN.