Topic       : MC56001 Documentation
Author      : JAY Software
Version     : 1.0 (19/11/1997)
Subject     : Programming/Assembler
Nodes       : 152
Index Size  : 4106
HCP-Version : 4
Compiled on : Atari
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View Ref-FileData ALU Input Registers (X1,X0,Y1,Y0)

    X1,X0,Y1, and Y0 are four 24-bit, general-purpose data registers. They
can be treated as four independent, 24-bit registers or as two 48-bit
registers called X and Y, develloped by the concatenation of X1:X0
and Y1:Y0, respectively. X1 is the most significant word in X and
Y1 is the most significant word in Y. The registers serve as input
buffer registers between the XDB or YDB and the MAC unit. They are used as
data ALU source operands, allowing new operands to be loaded for the next
instruction while the register contents are used by the current instruction.
The registers may also be read back out to the appropriate data bus to
implement memory-delay operations and save/restore operations for interrupt
service routines.