11.4.11 I/O Integrity Module (IOIM)
The I/O Integrity Monitor (IOIM) is typically used to monitor the integrity of a signal generated by any dsPIC/MCU. However, it can also be used to monitor any signal generated outside of the dsPIC/MCU by connecting the reference input and feedback inputs to the appropriate external monitoring points.
The purpose of the IOIM in dsPIC33A is to provide and meet safety component requirements for applications that require monitoring the connectivity of a selected reference signal against a feedback signal, along with the user configurable path delays. A typical application for the I/O Integrity Monitor is to compare the data supplied to an output pin with the data read from the output pin driver. The output pin driver data are supplied to the monitor via an input buffer. If desired, a second pin can be used to monitor the output pin data at a remote location, somewhere on the PCB or far from the chip.
Typical uses include:
- To increase protection for customers who are building safety-sensitive applications.
- To simplify structural tests for safety applications.
- To ensure the pin has been connected correctly in its final environment by using structural tests.
The IOIM detects a change in the reference signal to start the blanking timer, which is used to account for the feedback path delay. After a programmable amount of time, the state of the selected feedback input is compared with the state of the reference input. If a mismatch is sampled at any time or a configured time after the blanking period, an error event is generated through an interrupt. Every error event is used to increment the user-defined error counter value; the IOIM gives an overflow status bit once the error counter reaches the Overflow state.