Modern machine-control units are increasingly decentralized in their
assembly and have intelligent peripheries addressed by buses.
In addition to control of the overall system, the recognition of
failures and states on I/O lines is of growing importance as the desire
to minimize - or, where possible, totally avoid - costs for service and
This is a task that can be assigned to peripheral devices such as
the high-side driver iC-JX, which can simplify the monitoring and
handling of errors.
Figure 1 below shows iC-Haus
GmbH's iC-JX in a typical industrial application environment.
for use in industrial applications such as machine-control panels or
24V I/O modules, this device permits I/O functions to be completely
programmed by the microcontroller, enabling lamps or relays to be
driven, switches and sensors to be read out, and lines, drivers and
sensors to be monitored.
Communication with the microcontroller is achieved by either an SPI
or 8 bit parallel interface. In conjunction with an SPI, isolation for
the entire I/O system is possible by using only six optocouplers,
providing an inexpensive solution.
Without the need for additional components, up to four JX devices
can be addressed via the SPI, making a total of 64 I/O channels
1: The iC-JX allows I/O functions to be completely programmed by the
MCU control unit.
The iC-JX has 4x4 I/O ports that can be configured in blocks as
input or output channels. Bidirectional drivers record logic states
from external sources or read back the output state. This enables an
open wire or short circuit in the load to be recognized.
The high-side short-circuit-proof output channels permit various
loads of up to 150mA DC (500mA pulses) - including protection against
flyback. Integrated control logic identifies input signal changes and
generates an interrupt.
Each I/O has digital input filters for suppressing interference
(e.g. contact bouncing). By integrating previously discrete filter
components, the number of external devices is reduced, lowering costs.
2: The presence or specified values of connected loads can be checked
prior to activation.
Each I/O port comes equipped with programmable current sources so
that the presence or specified values of connected loads can be checked
prior to activation (Figure 2 above).
In addition, all ports have a common 10bit ADC at their disposal for
the evaluation of any sensors connected up to the device (Figure 3 below). This allows any
failures to be recognized, such as cable fractures or changes in the
characteristic curve of loads due to the effects of aging or excessive
3: A 10bit ADC evaluates sensors connected to the device.
Further application-specific functions are the definition of interrupt
sources, such as overcurrent, input levels and flash circuits, such as
those used in control panel displays.
The given interrupt sources can be modified by digital filters with
variable filter times. This allows impulsive input signals caused by
contact bouncing or high inrush currents with lamps and capacitive
loads to be masked, and keeps them from automatically triggering an
In return, all inputs have a Schmitt trigger characteristic so that
slow signals can also be processed reliably. The device has internal
protective circuitry governing the shutdown of drivers with under
voltage and excessive temperature, for example.
Each driver stage has its own temperature sensor, which is evaluated
in two stages, putting the microcontroller in the position of being
able to carefully shut down the chip if excessive temperature occurs.
A common inhibiting input permits all outputs to be shut down
externally, thus providing a security watchdog that is independent of
Thanks to its internal signal conditioning unit, iC-JX does away
with the need for external filter components. By integrating a signal
readback function, the device also allows for greater packaging density
while providing improved reliability and flexibility.
David Lin is an Application
Engineer at iC-Haus GmbH