dCS 904 User Manual

Manual for Software Version 1.5x and 1.36

dCS Ltd

June 2000

 

 

RS-232 Remote Control Interface

Overall Description

dCS 9xx units can be controlled using a simple serial protocol, via the RS-232 ports, using the control format described below. All commands available from the front panel (and a few others, dCS use only) of a unit can be remotely controlled using this approach. Each unit must have a unique ID (in the range 0 to 99) which must be set up by hand using the menu system on the front panel. The units remember their ID when powered down, so this setting up only has to be done once.

Physical Interface

Units are all connected in a RS-232 daisy chain, up to a maximum of 11 units, with a serial cable (DB9 pin female straight cable) connected between the Serial Out and Serial In ports of the units. The same type of cable is used to connect the Serial In port of the first unit on the chain to the COM port of a PC.

By default all units are configured to operate at 1200 baud. Standard RS-232 signal levels are used. Bytes are transmitted with 1 start bit, 8 message bits, 1 stop bit and no parity.

Units can be switched to 1200, 2400, 4800 or 9600 baud. An RS-232 break will reset all units on the daisy chain to 1200 baud. A special command and ID is used to configure the units to other baud rates (see “Special Commands and Protocols” below). The following rates are recommended:

3 or less units

4800 baud

4 to 7 units

2400 baud

8 to 11 units

1200 baud

Operation of the daisy chain at higher than the recommended rates may result in incorrect behaviour of the system – either because the units misinterpret commands, or, more likely, because the controlling computer misinterprets their replies. Units will revert back to 1200 baud if they are switched off and on - they do not remember what they were last set to.

9600 baud is currently not fully tested over all temperatures. It can be used for single units operating in a benign environment.

Timing Accuracy and Warnings

The units use clock dividers derived from their crystals to produce the RS-232 signals. The frequency of operation is measured to be better than 2% for all baud rates with both crystals. Some of the commands, however, switch clock frequencies, and these may be controlled by phase locked loops with long time constants. While this is happening, correct RS-232 timing cannot be guaranteed, and the units should not be addressed – a period of 30 secs should be allowed after switching clock frequencies for timings to stabilise.

Units acknowledge and repeat back their actions on receipt of a command. The acknowledge should be waited for and checked before proceeding to the next command – see Acknowledge Message below

Manual part no: DOC135904 iss 2B2

Page 53

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