Parker PDHX-E Series User Manual page 53

Unit 1 moves 25,000 steps, unit 2 moves 50,000 steps and unit 3 moves 100,000 steps. All
three units use the same acceleration and velocity rates.
Interactive operation with a PC/PLC
To create a reliable, trouble free interactive RS232 communications control program between
a PC/PLC and the serial interface you should note the following points :
• • Use the X-WARE package for terminal emulation on an IBM PC or equivalent
computer system.
• • The interface should only be operated in computer mode to suppress error messages
and extended text output.
• • The program should operate the interface with a response check during critical
processes, such as sequence download. The response check will need to detect :
• No response at all
• Incorrect characters
• More characters than expected
• Less characters than expected
• Control characters such as EOF caused by errors
• Correct response
The response expected should be either echoback, or character returned by interrogation
commands, or the sequence of the two.
• If there is no check for echoback on each character, you should include a delay of up to
1ms between each character sent . This may require characters to be sent individually
rather than as strings.
• You should not use the simple BASIC INPUT statement as this 'hangs' the link without
time out if an error causes no carriage-return character to be received from the interface.
• Interpreted BASIC should not be used, as it is too slow for most applications.
• Interrupt error handling, such as the BASIC 'ON ERROR" statement, should be enabled.
• Commands such as SV, Z, RFS and RIFS take several seconds to execute. This also
applies to status commands like DR and HELP. It is recommended you insert a suitable
delay after these commands to allow them to fully execute their intended function without
corrupting immediately following commands, although the use of these commands in an
interactive situation is unlikely.
• If problems arise the communications error responses actioned by the R command will
help diagnosis. In some cases a recovery can be attempted by sending the command
again (such as the R command itself). But this may not always be appropriate, for
example LD3 altered to L3 would not be fully corrected by simply sending LD3 again.
• A routine that breaks some of these rules may appear to work satisfactorily, but is not
necessarily safe. The worst case communications response condition may involve a
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