dCS 904 User Manual

Manual for Software Version 1.5x and 1.36

dCS Ltd

June 2000

 

 

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

00immediate (less than 50 msecs)

01up to 3 seconds

10up to 15 seconds

11up 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.

Manual part no: DOC135904 iss 2B2

Page 55

135904ma2b2.pdf file available from website

Contact dCS on + 44 1799 531 999

email to: more@dcsltd.co.uk

(inside the UK replace + 44 with 0)

web site: www.dcsltd.co.uk