> I think I might go the route of getting a 16f84 first, then moving to a
> 16f628.  Especially since a book a bought a while back only uses the 84.. :)

If those are your choices, do yourself a favor and start with the
16F628 instead of the 16F84. Conversion of any code you might
encounter in the book is relatively simple:

1. Change variables
The range of variables on the 16F628 start at 0x20 instead of 0x0C.
This means you will either have to:
a) do nothing, in case the book uses proper relocatable code.
b) change CBLOCK 0x0C into CBLOCK 0x20
c) change any register definition (EQU) pointing to a register between
0x0C and 0x1F to one that is higher or equal to 0x20.

2. Initialize CMCON register to change all pins to 16F84(A) configuration
This is done with the following code:
  movlw 0x07
  movwf CMCON
If you want you can put this between a check whether CMCON exists, in
which case the code will remain compatible with the 16F84.

3. With 1-2 you will fix most of the simple code. However, some code
for the 16F84 blithely assumes that registers are accessible
regardless of the settings of RP0 (and RP1). You can either fix this,
or, if you use less than 17 registers, make sure (in step 1) that all
registers point to 0x70 to 0x7F. Also, if the code uses an interrupt
routine and the interrupt routine ignores proper RP0 (and RP1)
setting, you will either need to add that to the interrupt routine, or
move all interrupt variables to the 0x70 to 0x7F region. See the
16F628(A) manual for a good way to save and restore variables from
interrupts properly.

4. If the code uses EEPROM, note that EEADR and EEDATA are no longer
in bank 0. This means that before accessing EEADR or EEDATA you will
need to do:
  banksel EEADR
and afterwards, when using a register in bank 0 again, you need to
  banksel <that register>
again. See the 16F628(A) manual for a good way to access EEPROM memory.

5. If the code uses the EEIE bit in INTCON, use EEIE from PIE1
instead, and make sure to surround it with the appropriate banksel
statements (see 4). The same counts for EEIF in INTCON, which moved to
PIR1.

6. Add _LVP_OFF to the CONFIG statement to free up RB4. If you want to
keep your electronics simpler too, you can also disable the reset pin
(in which case it doesn't need to be pulled up anymore) and use an
internal oscillator (in which case you don't need a crystal anymore).
Add the appropriate CONFIG bits for this, if you want, but make sure
your programmer/software will still work under that configuration.

This seems like a long list, but I also had a book that only use the
16F84A, and I discovered that very little needed to be changed, most
of the time. If you write your own programs, and they are not going to
use the limits of the particular PICmicro, it is recommended to NOT
use CBLOCK (and certainly not EQU) to give your registers names, but
instead use relocatable code.

Greetings,
Maarten Hofman.

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