MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 50

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

MC68000/MC68008 Core
where SCCE1 is equated to the actual address of SCCE1.
2-20
2. To clear bits 0 and 1 of SCC1, execute "MOVE.B #$03,SCCE1”
3. To clear all bits in SCCE1, execute "MOVE.B #$ff,SCCE1"
DO NOT use read-modify-write instructions to clear bits in an
event register, or ALL bits in that register will inadvertently be
cleared. Read-modify-write instructions include BSET, BCLR,
AND, OR, etc. These instructions read the contents of a location,
perform an operation, and write the result back, leaving the rest
of the bits unchanged. Thus, if a bit is a one when read, it will be
written back with a one, clearing that bit. For example, the in-
struction “BSET.B #0,SCCE1” will actually clear ALL bits in
SCCE1, not just bit 0.
MC68302 USER’S MANUAL
NOTE
MOTOROLA