Allen-Bradley 1794-ASB

The 1794-ASB module from Allen-Bradley is part of the FLEX I/O modular system. This system is composed by adapters/power supply, terminal bases and I/O modules. The 1794-ASB is an adapter/power supply whose purpose is to power the internal logic of the system and the I/O modules. This model can support as much as 8 I/O modules. The adapter transfers data from the controller to the discrete I/O and viceversa every flexbus scan and analog data can be transfered using BTW and BTR instructioon in LD programs. The system runs on 24 volts DC power and provides wiring connections for power supply on the bottom of the device. The module has four diagnostic indicators on the front of the system that provide the user some feedback on the system operations. Two green indicators provide feedback on whether the system has power and whether the adapter is active and running. The two red indicators are used to provide the user some feedback on adapter or local faults. The system also has a reset pushbutton to reset any fault of the system. The module supports 5 modes of addressing: a standard mode that allows input and output data for digital modules, a compact mode and a complementary mode, for which either input or output data may be available for the digital I/Os, but not both. The system power dissipation can reach a maximum of 4.6 watt and its current draw should be around 330 milliampere at 24 volts DC and around of 730 milliampere at 12 volts DC.

The 1794-ASB Flex I/O adapter module is used to establish communication between different types of programmable controllers and I/O modules through remote I/O networks. Supported programmable controllers include Allen-Bradley legacy controllers such as PLC2, PLC3, and PLC5, SLC500, as well as modern Logix controller platforms and various third-party devices. Up to 8 I/O modules can be connected simultaneously to the adapter. The adapter transmits data to the I/O modules through Block Transfer Write (BTW) instruction and receives data from the I/O modules through Block Transfer Read (BTR) instruction. The supported data transfer rates are 57.6 Kilobits per second (Kbps), 115.2 Kilobits per second (Kbps), and 230.4 Kilobits per second (Kbps). The data transfer takes place on every flexbus scan which keeps the controller updated all the time. The main components of the 1794-ASB are diagnostics indicators, communication reset button, remote I/O connection interface, Direct Current supply voltage connection ports, Flexbus connector, and Addressing mode switches. The indicators show four different states: Power ON, Adapter ACTIVE, Adapter FAULT, and LOCAL FAULT. The communication reset button is used to solve communication errors whenever occur. The remote I/O interface is used to connect the programmable controller to the adapter. The Belden 9463 or equivalent cables are used to accomplish the interfacing. A 24 Volts Direct Current (VDC) supply is applied through the voltage connection ports. The adapter draws the required operating current of 450 milliamperes (mA) from this source when all the 8 I/O modules are connected. The Addressing mode switches consist of two 8-position switch assemblies that are used for: starting the I/O group, defining the I/O rack number, enabling the memory image hold inputs, selecting the rack fault switch, addressing the operation modes for the adapter (8-point/16-point/32-point), setting up the communication rate, controlling the processor restart lockout and controlling the hold last state.