Intel 8253 - Description of the Modes; Register File

XA User Guide 6-2 4/17/98
6.2 Description of the Modes
6.2.1 Register Addressing
Instructions using this addressing mode contain a field that addresses the Register File that
contains an operand. The Register file is byte
2
, word, double-word or bit addressable.
Example: ADD R6, R4 Before: R4 contains 005Ah
R6 contains A5A5h
After: R4 contains 005Ah
R6 contains A5FFh
Figure 6.1
2. The unimplemented 8 word registers are not Byte addressable
ALU
ADD R6, R4
REGISTER - REGISTER
REGISTER FILE
DESTINATION
R6
R4
SOURCE
005Ah
A5FFh (result)
A5A5h (original contents)