28 Deadman Timer (DMT)

Note: This data sheet summarizes the features of the dsPIC33CK512MPT608 family of devices. It is not intended to be a comprehensive reference source. To complement the information in this data sheet, refer to “Deadman Timer (DMT)” (www.microchip.com/DS70005155) in the “dsPIC33/PIC24 Family Reference Manual”.

The primary function of the Deadman Timer (DMT) is to interrupt the processor in the event of a software malfunction. The DMT, which works on the system clock, is a free-running instruction fetch timer, which is clocked whenever an instruction fetch occurs, until a count match occurs. Instructions are not fetched when the processor is in Sleep mode.

DMT can be enabled in the Configuration fuse or by software in the DMTCON register by setting the ON bit. The DMT consists of a 32-bit counter with a time-out count match value, as specified by the two 16-bit Configuration Fuse registers: FDMTCNTL and FDMTCNTH.

A DMT is typically used in mission-critical and safety-critical applications, where any single failure of the software functionality and sequencing must be detected.

Figure 28-1 shows a block diagram of the Deadman Timer module.

Figure 28-1. Deadman Timer Block Diagram
Note:
  1. DMT Max Count is controlled by the initial value of the FDMTCNTL and FDMTCNTH Configuration registers.
  2. DMT window interval is controlled by the value of the FDMTIVTL and FDMTIVTH Configuration registers.