Allen-Bradley 1785-L20B

The Allen-Bradley PLC-5 processors have ports configurable for either a Data Highway Plus messaging communication link or a Universal Remote I/O link. As a Universal Remote I/O port, it can be configured as either an I/O scanner port or an I/O adapter port. As an I/O scanner port, it monitors and controls the I/O on the link by communicating with the I/O adapters for those I/O. As an adapter port, it communicates only with the I/O scanner port on the link, passing a maximum of one I/O rack of input and output data between the two to provide distributed processing.

The scanner-mode PLC-5 controller can:- gather data from node adapter devices in remote I/O racks - process I/O data from 8-, 16-, or 32-point I/O modules- address I/O in 2-, 1-, or 1/2-slot I/O groups- support a complementary I/O configuration - support block-transfer in any I/O chassis - ladder logic program using a language that is representative of relay logic.- performing diagnostics- programming discrete control

Use the 1785 for subroutines for storing recurring sections of program logic that can be accessed from multiple program files. A subroutine saves memory because you program repetitive logic only once. The JSR instruction directs the controller to go to a separate subroutine file within the logic controller, scan that subroutine file once, and return to the point of departure.

Main Control Programs (MCPs)
Separate sequential logic from ladder logic and structured text as a way of modularized your process and making troubleshooting easier. Use several main control programs (MCPs) to define one main control program for each particular machine or function of your process. MCPs accommodate independent or non-sequential activities.