| 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.
The long timeout is usable with the randomised periodic transmission
mode (101), as the 3 second timeout is longer than the longest
delay between transmissions in this mode.
Versions of the chip can be supplied with this period extended
to suit customer requirements
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