CONTREX CX-1010 - Manual (Page 5)

When the PLC wishes to relinquish control to the operator, it simply sends an
"unreasonable" setpoint value to the CX1010. Usually you choose a very large number,
(all 9's). This number must be in excess of the allowable max setpoint parameter. The
CX1010 rejects that setpoint, and retains the present or existing setpoint (presumably the
value entered by the operator). This technique addresses the fact that the polling list, or
polling action, is not easily modified on-the-fly. It is easier to just substitute the
"unreasonable" number for the polled parameter value. The PLC can also use this
technique to monitor the operator's manually entered setpoints. By reading the operator's
entry, the PLC can over-write it with a different number if it is determined that the
operator entered an inappropriate value.
Change from CX1000 (Ext Power Supply Requirement):
The CX1010 implements DeviceNet with the same software routines as did the CX1000.
However, there is a Hardware difference. The DeviceNet option card requires more
power (the spec says 250ma at 5vdc, but it actually draws less) than is available from the
controller. This power requirement (applied at JB2) is for the on-board processor, and
should not be confused with the normal external 24vdc power that runs the DeviceNet
network itself (applied at JB1). We have always recommended an external power supply
at 5vdc, 300 ma. However, the CX1000 had a 5vdc accessory supply rated at 200ma
that was often used in spite of our recommendation. The CX1010 does NOT have a 5vdc
accessory supply, but now has a 12vdc supply that is intended for encoder use. This
12vdc is NOT acceptable for the DeviceNet card. An external supply is required. You
may use any brand or style, but for reference, you could use DigiKey catalog number
T309-ND, rated 300ma at 5vdc +/- 5% at approx $10 cost.
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