Commodore Plus 4 - Page 266

254 Machine Language on the Commodore Plus/4
OLD—Clear Decimal Mode
The processor is put in normal hexadecimal mode.
Operation: 0-+ D Flags Affected: D
Addressing Mode Syntax Opcode Bytes Cycles
Implied CLD D8 1 2
See the section on decimal mode.
Example: This program places the processor into decimal mode and adds the contents of
$2100 and $2101. The result is placed in $2102. Decimal mode is terminated using
the CLD instruction.
. 2000 P8 SED Put the processor into decimal mode.
. 2001 18 CLC Prepare to add.
. 2002 AD 00 SI LDA $2100 Get the first decimal value.
. 2005 6D 01 21 ADC $2101 Add the second decimal value.
. 2008 8D 02 21 STA $2102 Store the result.
. 200B D8 CLD Exit decimal mode.
. 200C 00 BRK Stop processing.
Use the M (Memory) command to examine and change the contents of
$2100-$2102 to experiment with decimal mode addition.
CLI—Clear Interrupt Disable Flag
The interrupt disable flag is cleared, which allows interrupts to occur.
Operation: 0 -> / Flags Affected: I
Addressing Mode Syntax Opcode Bytes Cycles
Implied CLI 58 1 2
Example: This example alters the IRQ vector. Before executing it, check the default
contents of $0314-$0315 with the M (Memory) command. The low byte of the
default address for IRQ processing is located in $0314 and the high byte in $0315.
If this address is not $CE0E, replace the $CE0E in the program with it.
. 2000 78 SEI Disables the interrupts.