Hi All,

I've been busily building a CRC checker for a mag. tape data stream
using a 17C42. (17C42-25/JW)

During development I have come across a number of questions that I
have had difficulty answering maily caused by the programmer I'm using.

1.  I am using an ICE TECHNOLOGY Micromaster LV programmer, and the
    parameters suppied in the library with the programmer for the 17C42
    says that Vpp is 11v, not 13v as in the '95 data book.

    I have contacted ICE and they have told me that a Vpp of 11v
    is acceptable using the 'new' algorithm supplied to them by
    Microchip.

    A number of times now, I have had a chip 'on test' for a few days
    which is o.k. at first and then fails.  The failure is due to a bit
    becoming 'unprogrammed'.  Anything to do with the low Vpp or the
    'new' algorithm?  (This problem has appeared in different
    batches of chips)

2.  First 'shock' with the above programmer was that the
    configuration fuses are not supported in the hex.  ICE said that
    in advance information from Microchip has told them not to bother
    support this feature as they [microchip] don't believe it is the
    way to go.

    However, the '95 data book "clearly" (in a fuzzy grey box!)
    say they Microchip see this feature as been on great benefit to the
    customer.

    What's the verdict, MChip?

3.  I seem to have lost the thread on the 17C42-JW paperweight saga.
    Does the 17C42-JW Rev C silicon have an OTP code protect fuse?
    I have talked to a guy in the U.K. office of MChip who thinks that
    OTP code protect fuses on UV erasable devices are the way to go
    because its "very secure" but he still can tell me why because the
    "Factory don't allow them to speak about security issues" although
    he said he would find out why it was a good idea and let me know
    in a week or so.  Any one got any better answers?

4.  I've had a lot of problems getting MPSIM to simulate an interrupt
    from timer 1/2 when configured as a 16 bit timer.  Checked
    everything I could, but I can still watch the counter values
    increment & reach the roll-over value & then reset to count
    up again, but the overflow bit does not get set in the
    interrupt register.  I'm using a version of MPSIM I
    downloaded in June this year, anyone else have this problem, or is
    it too many later nights?



Thanking you in anticipation,

    Ian Houldridge