Inputs, Processing, Outputs

INPUTS, PROCESSING, OUTPUTS







All modern, microprocessor-controlled systems use various sensors, switches, voltage signal circuits, ground signal circuits, etc. to provide information to a system control module or "brain." These sensors, switches, and other components are known as the input devices; the information or signals they provide are known simply as the inputs. Typically, each input has its own, dedicated terminal or pin at the control module.

Some examples of inputs to the climate control system control module are:
- heater core temperatures (from the heater core temperature sensors)
- evaporator temperature (from the evaporator temperature sensor)
- refrigerant pressure (from the compound pressure switch on the receiver/dryer)
- stratified air thumbwheel position (from the thumbwheel potentiometer)
- vehicle speed (from the vehicle speed sensor)
- A/C compressor request (from the A/C compressor "snowflake" button)
- the start signal, KI. 50 (from the ignition switch).

The system control module or "brain" repetitively accepts all the inputs (many times each second) and processes them. In other words, the module "looks" repeatedly at the information it receives, "thinks" about what it means, and "decides" what it should do.

Of course, the control module doesn't actually think. What really happens is that all the thinking has been done ahead of time, during the control module (and system) development phase. Engineers and researchers thought about how the module should respond to specific inputs, combinations of inputs, or even missing inputs, and then programmed the control module microprocessor to do what they wanted it to do in each case.







Each time the control module processes the inputs and "decides" what to do, it provides power or ground circuits to operate solenoids, stepper motors, relays, lamps, etc., or it may send signals to other control modules. The signals or power/ground circuits provided by the control module are known as its outputs. The actual component operated (relay, solenoid, motor, etc.) is referred to as the output device.







Control modules typically contain several processing areas, which use specific inputs and process them to control specific outputs. In other words, although the module seems to be performing several tasks at once, it doesn't "lump all the inputs together" to control all the outputs.







As an example, on IHKR1 climate control Systems (1989 E34), the IHKR control module operates both the blower motor and the water valves (and a lot of other things, too).
- The Input used to control blower speed (an output) is the blower speed knob position input, which goes to the processing area for blower speed control. If the input device is faulty, or the circuit is broken, the blower control processing area won 1t get all the information it needs to make decisions and it won't work properly.
- The water valve control processing area, however, which doesn't use the blower speed knob position input, won't notice that it is missing and will continue to function normally.

To perform diagnosis efficiently, it's important to understand which inputs are used to control a specific output. Or perhaps more importantly, which inputs will not affect a specific output.

BMW uses Inputs, Processing, Outputs diagrams (IPOs) to provide a quick view of the important features of microprocessor controlled systems. Typically (as shown in the previous graphics), inputs are shown on the left side of the IPO, the processor (control module) is shown in the middle, and the outputs are shown on the right.

The inputs, processing, outputs diagram (IPO) for the E32 IHKA climate control system is shown on the facing page.