PLC Inputs and Outputs
This article will discuss about Analog inputs and outputs with PLC-5. The PLC-5 logic ladder will be shown on figure at below. It will control an analog input card. The Block Transfer Write (BTW) will end configuration data from integer memory to analog card in rack 0, slot 0. The data from N7:30 to N7:66 describe the configuration for different input channels. Once the analog input card receives this it will start doing analog conversions.
This instruction is edge triggered, so it is run with the first scan, but the input is turned off while it is active, BT10:0/EN. This instruction will require multiple scans before all of the data has been written to the card.
The Block Transfer Read (BTR) will retrieve data from the card and store it in memory N7:10 to N7:29. This data will contain analog input values.
The PLC-5 ladder logic at figure below can be used to set analog output voltages with 1771-OFE Analog Output Card. The BTW instruction will write configuration memory to the card. Values also can be read back from the card using a BTR, but it is only valuable when checking the status of the card and detecting errors. The BTW is edge triggered so the BT10:0/EN input prevent the BTW from restarting the instruction until the previous block has been sent. The MOV instruction will change the output value channel 1 on the card.