You raise a good question. Looking into it further, there is no difference. I looked at the data sheet, and it says you have 8 options:
Code:
111 = RC oscillator: CLKOUT function on RA6/OSC2/CLKOUT pin, Resistor and Capacitor on RA7/OSC1/CLKIN
110 = RC oscillator: I/O function on RA6/OSC2/CLKOUT pin, Resistor and Capacitor on RA7/OSC1/CLKIN
101 = INTOSC oscillator: CLKOUT function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN
100 = INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN
011 = EC: I/O function on RA6/OSC2/CLKOUT pin, CLKIN on RA7/OSC1/CLKIN
010 = HS oscillator: High-speed crystal/resonator on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN
001 = XT oscillator: Crystal/resonator on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN
000 = LP oscillator: Low-power crystal on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN
Then looking at the .info file, it shows 20 options, which doesn't quite make sense. Looking closer, we have to look into the microchip .inc files, located here: C:\Program Files (x86)\Microchip\MPASM Suite\P16F628A.inc
Here there are 3 internal options with no clockout which all have the same EQU number.
Code:
_FOSC_INTOSCIO EQU H'3FFC' ; INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN
_INTOSC_OSC_NOCLKOUT EQU H'3FFC' ; INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN
_INTRC_OSC_NOCLKOUT EQU H'3FFC' ; INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN
So, I guess you can use any one of the above and get the same result.
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