Freescale Semiconductor MC68HC908MR32 - Manual (Page 137)

Fault Protection
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 137
12.6 Fault Protection
Conditions may arise in the external drive circuitry which require that the PWM signals become inactive
immediately, such as an overcurrent fault condition. Furthermore, it may be desirable to selectively
disable PWM(s) solely with software.
One or more PWM pins can be disabled (forced to their inactive state) by applying a logic high to any of
the four external fault pins or by writing a logic high to either of the disable bits (DISX and DISY in PWM
control register 1).
Figure 12-26 shows the structure of the PWM disabling scheme. While the PWM pins
are disabled, they are forced to their inactive state. The PWM generator continues to run — only the
output pins are disabled.
To allow for different motor configurations and the controlling of more than one motor, the PWM disabling
function is organized as two banks, bank X and bank Y. Bank information combines with information from
the disable mapping register to allow selective PWM disabling. Fault pin 1, fault pin 2, and PWM disable
bit X constitute the disabling function of bank X. Fault pin 3, fault pin 4, and PWM disable bit Y constitute
the disabling function of bank Y.
Figure 12-25 and Figure 12-27 show the disable mapping write-once
register and the decoding scheme of the bank which selectively disables PWM(s). When all bits of the
disable mapping register are set, any disable condition will disable all PWMs.
A fault can also generate a CPU interrupt. Each fault pin has its own interrupt vector.
12.6.1 Fault Condition Input Pins
A logic high level on a fault pin disables the respective PWM(s) determined by the bank and the disable
mapping register. Each fault pin incorporates a filter to assist in rejecting spurious faults. All of the external
fault pins are software-configurable to re-enable the PWMs either with the fault pin (automatic mode) or
with software (manual mode). Each fault pin has an associated FMODE bit to control the PWM
re-enabling method. Automatic mode is selected by setting the FMODEx bit in the fault control register.
Manual mode is selected when FMODEx is clear.
Address: $0037
Bit 7 6 5 4 3 2 1 Bit 0
Read:
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Write:
Reset: 1 1 1 1 1 1 1 1
Figure 12-25. PWM Disable Mapping Write-Once Register (DISMAP)