Originally Posted by
gw1
A is a hardware feature of many microcontrollers and embedded systems (eg arcade video games) for purpose of automatically rebooting if software hangs. It's analogous to a . When watchdog is enabled the program must perform a particular instruction sequence at certain periodic times otherwise a reset will occur.
Most smartcard applications don't use watchdog feature, and consequently are configured with watchdog fuse turned off. If you override the setting and manually enable the watchdog then you'll find the card won't work, unless the application was written to look after the watchdog timer.
The power up fuse (PWRTE) is a feature of PIC processors that causes the processor to wait for a short time, about 72ms, after the reset pulse before starting to execute instructions. The feature exists to accommodate systems with slow starting oscillators; if processors start executing before the clock has settled malfunction and crashes can occur. In DVB CA emulator applications you need to leave this fuse turned off. The ISO7816 specification already ensures clock is stable before reset, so the delay isn't needed. More importantly, some receivers will deem the card to be dead if they don't receive the ATR within 20-30ms.
The fuse settings are usually specified by the programmer in his source code and stored in the code hex file generated by the compiler. Card programming tools such as ICProg, once you've specified the processor type (eg PIC 16F876 for silver or 16F84 for gold), will usually adjust the on-screen fuse controls to the application's intended settings when you open the code hex file. In rare occasions you may find hex files that don't contain fuse settings, and in such cases you sometimes need to adjust the fuses manually for the application to work properly. But normally you needn't worry about that unless others using the application tell you otherwise.
You can find full description of fuses by reading the datasheet for the card processor. Eg For Gold the 16F84 data sheet is [1.5MB PDF] and the fuses (aka configuration bits) are explained in section 6. For Silver the 16F876 data sheet is [3.7MB PDF] and the fuses are explained in section 12.
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