Hello PIC users


I have been on the PICLIST for some time now, but this is my first
posting because I haven't had much time. First a short introduction:
I'm an EE student in my last term - I hope :)  I live in Denmark and
have been working with PIC's since 1991.

One of my first PIC projects was to write an assembler since the
tools Microchip provides were (and still are) slow, buggy and
generally user unfriendly.
The first version was a command line program, but soon it became an
Borland-like IDE (Integrated Development Environment) with menus,
multi-file editor, etc.
The next step was to add a simulator/debugger. This gave me some
problems, because Microchips manuals doesn't tell all you need to
know. In some cases the manuals are even misleading.
Some of the tricky areas are RTCC synchronization, interrupts and
A/D timing (in PIC16C71).

To get the information I need, I have written some small programs,
and tested them on the real thing (i.e. PIC's). This means that my
debugger behaves exactly like the hardware, which is more than I
can say for any other debuggers I have worked with (Microchip,
Transdata etc.).
I have also found a bug with the TO (TimeOut) bit in the Status
register. Sometimes the bit is not set correctly after a MCLR reset.
If anybody is interested I can post some more info.

Currently I'm working on PIC16C84 support for the debugger, and I
found some "features" regarding the data EEPROM: When you want to
write to the EEPROM, you have to set up the address (EEADR) and
data (EEDATA) and then execute the following sequence:

    MOVLW   55h
    MOVWF   EECON2
    MOVLW   0AAh
    MOVWF   EECON2
    BSF     EECON1,WR

to initiate the self timed erase/write cycle. (and of course the
write enable (WREN) bit must have been set).
This rather awkward procedure is used to minimize the risk of
unintended writes to the data EEPROM, which may hold important data.

BUT... What happens if you change the EEADR after the erase/write cycle
has been started ?
To test, I wrote a program that initiated a write and then incremented
the EEADR register every 0.5ms. Result: 4 (!) EEPROM locations were
erased and the data was written into a 5. location...
Looks like Microchip forgot an address latch.


Michael Brinks