Wednesday, January 4, 2012

Variable Data PLC-2 for Triggering Messages

This case demonstrates how the message that using a value of variable data from a Programmable Controller of PLC-2 can be showed in the DL20. There are ten lines of data, D0-D9, and two lines of strobe, MS0 and MS1, in the DL20. It designates on the DL20 that the rate offer on the lines of data D0 - D9 is a number of message to be activated if both MS0 and MS1 are high. At this case all 10 data lines, D0-D9, are inspected. If data of binary message is chosen in the menu of DL20, the range is 1 to 1022. If data of BCD message is chosen, the range is 1 to 399.

The DL20 shows data variable from the programmable controller in the range of 0 to ±32, 0 to 9999 BCD or 767 binary. As these are sixteen bit of values data and the DL20 have only ten lines of data, every variable have to be strobed in the DL20 in two parts at same time. Initially the high byte is strobe in. It is designated by set the strobe bit MS1 high and MS0 low.

This is designated by setting the strobe bit MS1 low and MS0 high. When a message is formed on the DL20 a symbol of variable data = or O can be located anywhere, and up to 20 times, within a message by pushing the key of [Ctrl] and [V] or [X] together. For the Industrial Terminal of 1770-T3, they have to be pressed in sequence. Control X is for variables of decimal point and/or fixed format variables and of Control V is for variables of non-decimal point. The programmable controller has to serially strobe the variables into the data queue of DL20 in the similar order that the variables are to show in the message. Subsequent to the variables are queued, after that the message number is activated. The below program example utilizes an instruction of sequencer output from the PLC-2 to strobe the information into the parallel port of DL20.

The sequencer instruction steps can be seen on the Industrial Terminal of 1770-T3 by moving the cursor to the instruction of sequencer and pushing 1 for display format of BCD or 0 for display format of binary. The NULL STEPS displayed in the above sequence are additional to assure requirements timing of the DL20.

The steps 1 through 8 appear above correspond to word 037-046 (octal) as described in the instruction of sequencer. The message would be shown as below:
TIMER 032 = 1234

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