PAGE
18
20
JUN
2005
WCM802/900
Binary Commands
Sending and receiving register values using binary commands is the fastest way to change the
operating parameters of the module. Binary commands are used most often to sample the signal
strength (RS command) and/or error counts or change module address and channels for polling
systems when a quick response is necessary. Since the sending and receiving register values
takes place through the same serial data path as 'live' data (received RF payload), interference
between the two can be a concern.
Common questions about using binary command mode:
•
What are the implications of asserting CMD in any of the various states while live data is
being sent or received?
•
Specifically, is there a minimum time delay after serial data is sent before which we can
assert CMD and send a command?
•
Is a delay required after CMD is de-asserted before we can send normal data?
•
How can we know if data being received is the response from a command or live data?
Answers: The CMD line can be asserted to send a command to the radio anytime during
transmission or reception of data. Note that the status of the CMD signal is only checked at the
end of the stop bit as the byte is shifted into the serial port. If the command is sent in the middle
of a stream of payload data to be transmitted, the command will essentially be executed in the
order it is received. If the radio is continuously receiving data, the radio will wait for a break in
the received data before executing the command. The
signal will frame the response coming
from the binary command request (see graphic below).
CMD (pin 5) must be asserted in order to send binary commands to an WCM802 / WCM900
Module. CMD can be asserted to recognize commands anytime during transmission or reception
of data. A minimum time delay of 100 µs (after the stop bit of the command byte has been sent)
must be observed before pin 5 can be de-asserted. The command executes after all parameters
associated with the command have been sent. If all parameters are not received within 0.5
seconds, the module aborts the command and returns to Idle Mode. Note: When parameters are
sent, they are always two bytes long with the least significant byte sent first.
Commands can be queried for their current value by sending the command logically ORed with
the value 0x80 (hexadecimal) with CMD asserted. When the binary value is sent (with no
parameters), the current value of the command parameter is sent back through the DO pin.
Figure
2.10.
Binary
Command
Write
then
Read
Signal
#4
is
CMD
(pin
5)
Signal
#1
is
the
DIN
(pin
4)
signal
to
the
radio
Signal
#2
is
the
DOUT
(pin
3)
signal
from
the
radio
Signal
#3
is
(pin
1)
A value was written to a register and then read out to verify it. While not in the middle of other
received data, note that the signal outlines the data response out of the module.
IMPORTANT:
For the WCM802 / WCM900 Module to recognize a binary command, RT (DI2
Configuration) Command must be issued. If binary programming is not enabled
(RT
≠
1), the module will not recognize that the CMD pin (Pin 5) is asserted and
therefore will not recognize the data as binary commands.