Which modes to use?
The CTA88 have a variety of operating modes. These are better understood by relating them to different
applications:
1. Wire replacment:. Operate transmitter in mode 010 (continuous: allows the STB output to be used as a
'good link' indicator) and receiver in mode 001.
If receiver operates in latched (011) mode then 'chattering' of the output is reduced (at extreme range, or with
interferers present), but the link is no longer fail safe
Latched mode is also compatible with send on change (011)
2. Momentary push buttons: Transmitter in mode 100 (send while any input is high), receiver in 001.
Outputs remain high for as long as the button is held down. This is the mode one would choose to control
(for instance) a pan/tilt head (D0= slew left, D1 = slew right, etc)
3. Controlling four lights: Use transmit mode 100 (send while high) or 011 (send on change), with the
receiver in mode 100. This gives four outputs (D0-D3), each set by one transmitter input (D0-D3) and reset
by another (D4-D7)
4. Monitoring infrequent events (such as door open/shut): Use transmitter in periodic transmit (101, to
keep channel occupancy and power usage low), and receiver on 010 (3 second timeout), 011 (hold last
burst) or 110 (serial data output, to a PC or data logging device).
In this mode the transmit duty cycle is less than 10% on average, and the variable delay between bursts
permits same channel operation of several CTA88 links with minimum transmit collisions
5. Send burst on trigger event: Set transmitter to mode 000 (off) and use C0 line high as a 'strobe' line. A
pulse between 100uS and 25mS with initiate a single transmission.
This gives an idea of the usable combinations, but with a little imagination others will be found
Incompatibilities: Certain operating modes are not compatible with some of the others:
RX 101 (toggle) doesn't work with TX 101 (periodic send) as the outputs switch on and off at the send rate
RX 100 (set and reset) doesn't work with TX 101 (as the response is sluggish) and doesn't need TX 010
(constant)
RX 101 (toggle) is also not best suited to extreme range operation, where the initiation can be a little
sporadic.
(At extreme range, latched (011) or set/reset (100) are the best receiver modes, combined with TX 100 (send
on any '1') as in this mode the failure of any single burst to be received matters less, as the operator can
continue to operate the transmitter until the receiver actuates )
Serial operation: The CTA88 is capable of a very simple, single byte, serial link operation. It is selected by a
'110' mode input.
This function is mainly intended for diagnostic work in the lab, but it does allow a pc to send or receive
CTA88 command bursts. Address is still selected by the parallel inputs
On the RX:
D4 = 'true' RS232 output
(+ve = low (0), 0V = idle/mark state)
D5 = 'inverted' RS232 output (+ve = idle/'mark' (1) state)
D6 : high for 500uS before, and during, serial byte output
On the TX
D4 = RS232 input
D5 : low = set 'true' input polarity, high = set 'inverted' input polarity
In all cases a single 9600 baud byte is received or sent.
The link is not transparent: on the TX end the 'tx on' pin can be used as a 'busy' output
Timeout: In modes 001 and 010, the receiver outputs the last received data for a given period, before
resetting D0-D7.
Any subsequent transmission will over-ride the current output state and reset the timer, even if the timeout
period has not expired.
The short period is set to be slightly longer than the time between consecutive transmit bursts in a
continuous mode.
Radiometrix Ltd
CTA28 Demo board
page 6
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