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dCS 954 User Manual Manual for Standard Software Version 1.5x
dCS Ltd June 2000
Manual part no: DOC136954 iss 2B1
Page 58
file 135954ma2b1.pdf available from website
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dCS
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The checksum is the sum of the bytes in the parameter list (bytes 5 to (last-1)
byte) modulo 256. The minimum length of an acknowledge message is 1 byte,
maximum 64. If the checksum is incorrect the transmitter should re-issue the
command.
For the first byte, the response times are:
xx
00 immediate (less than 50 msecs)
01 up to 3 seconds
10 up to 15 seconds
11 up to 25 seconds
The receiving unit will ignore any transactions on the RS-232 while it is busy. If
the transmitter sends commands to a unit when the unit is busy the unit will not
send an acknowledge back. The transmitter must be designed to time out after
50 msec and repeat the command if necessary. In a multi-unit environment, it
would be sensible to organise the transmitter to access units with a “round
robin” polling scheme – in this way several units can be instructed to perform
commands simultaneously, the transmitter coming back to busy units
periodically. It is also recommended that units are not accessed for the first ¾
of their “response” time – nothing untoward will happen, but the unit will be
ignoring the RS-232 and will not respond, so the transmitter would just time out
anyway.
Example : -
To set unit 2 Emphasis to AUTO using the RS-232 control format:
transmit the string [2][34][1][0][0],
and the receiving unit will respond [169].
Special Commands and Protocols -
BREAK
Continuous high on transmit line for more than 100 msec. Resets ALL units on
daisy chain to 1200 baud.
GLOBAL ADDRESSES
Address F0 hex (240 decimal)
ALL units on daisy chain react to command. Nothing acknowledges. This
should only be used for setting baud rates to 2400, 4800 or 9600 baud. Never
change baud rate from a higher rate to a lower rate, as this could result in
unexpected behaviour, always reset the daisy chain to 1200 baud and then
issue the appropriate command. Never change the baud rate of a single unit in
a multi-unit daisy chain as this could result in the chain locking up.
Address F1 hex (241 decimal), Command RS_ENABLE_DEBUG (19 decimal)
ALL units on daisy chain react to command. Nothing acknowledges. This
enables dCS debugging commands. This may result in unstable behaviour of
the unit.