Commodore Plus 4 - Page 275

The 6502 Microprocessor 263
The speed of the flashing can be changed by changing which bit of the jiffy
clock is examined at $200C and $2012.
INC—Increment Memory "by 1
The value currently in the operand is incremented by 1.
Operation: M + 1
Addressing Mode
Zero page
Zero page, X
Absolute
Absolute, X
- M
Syntax
INC $hh
INC $hh,X
INC $hhhh
INC $hhhh,X
Op
E6
F6
EE
FE
Flags Affected: N, Z
>de Bytes Cycles
2
2
3
3
5
6
6
7
The value stored in the operand is increased by 1. If the result is negative, the N
flag is set to 1; otherwise it is cleared to 0. If the result is zero, the Z flag is set to 1;
otherwise it is cleared to 0. It should be noted that the carry flag is NOT affected.
That is, an increment from $FF to $00 does NOT result in the carry flag being set.
Example: The upper left screen location is cycled through all of the available screen codes.
The INC instruction is used to update the character.
2000 A2 00 LDX #$00
2002 EE 00 OC INC #0000
2005 A5 A5 LDA $A5
2007 29 02
2009 DO FA
200B A5 A5
200D 29 02
200P FO FA
2011 CA
2012 DO EE
2014 00
AND #102
BNE 12005
LDA $A5
AND #$02
BEQ I200B
DEX
BNE $2002
BRK
.X counts the 256 screen codes.
Increment the upper left screen code
by 1.
Now wait. Get the value in the jiffy
clock.
Look at bit 1.
Wait until it is off.
Get the value in the jiffy clock.
Look at bit 1.
Wait until it is on.
Decrement the counter.
If not done, continue.
Stop processing.
The speed of the updating can be changed by changing which bit of the jiffy
clock is examined at $2007 and $200D.