Floating Point Instructions
MOTOROLA M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL 5-13
FADD Floating-Point Add FADD
(MC6888X, MC68040)
If R/M = 1, specifies the location of the source operand location. Only data
addressing modes can be used as listed in the following table:
*Only if < fmt > is byte, word, long, or single.
R/M field—Specifies the source operand address mode.
0 — The operation is register to register.
1 — The operation is < ea > to register.
Source Specifier field—Specifies the source register or data format.
If R/M = 0, specifies the source floating-point data register.
If R/M = 1, specifies the source data format:
000 —Long-Word Integer (L)
001 —Single-Precision Real (S)
010 —Extended-Precision Real (X)
011 — Packed-Decimal Real (P)*
100 —Word Integer (W)
101 —Double-Precision Real (D)
110 — Byte Integer (B)
*This encoding will cause an unimplemented data type exception to allow
emulation in software.
Destination Register field—Specifies the destination floating- point data register.
Opmode field—Specifies the instruction and rounding precision.
Addressing Mode Mode Register Addressing Mode Mode Register
Dn 000 reg. number:Dn (xxx).W 111 000
An — — (xxx).L 111 001
(An) 010 reg. number:An # < data > 111 100
(An) + 011 reg. number:An
– (An) 100 reg. number:An
(d
16
,An) 101 reg. number:An (d
16
,PC) 111 010
(d
8
,An,Xn) 110 reg. number:An (d
8
,PC,Xn) 111 011
(bd,An,Xn) 110 reg. number:An (bd,PC,Xn) 111 011
([bd,An,Xn],od) 110 reg. number:An ([bd,PC,Xn],od) 111 011
([bd,An],Xn,od) 110 reg. number:An ([bd,PC],Xn,od) 111 011
0100010 FADD Rounding precision specified by the floating-point control
register.
1100010 FSADD Single-precision rounding specified.
1100110 FDADD Double-precision rounding specified.
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