AT75C datasheet(35/171 Pages) ATMEL

35 / 171 page

AT75C DSP Subsystem

1368C–INTAP–08/02

contents of the P register remain unchanged. At two multiply instructions, maa

and maasu, the P register is also aligned, i.e., after the P register is sign-

extended and shifted according to the PS field, it is also shifted by 16 to the right.

All move instructions using the accumulator (aX or bX) as a destination are sign-

extended.

All instructions that use the accumulator-low (aXl or bXl) as a destination will clear

the accumulator-high and the accumulator extension. Therefore, they are sign

extension-suppressed.

All instructions using the accumulator-high (aXh or bXh) as a destination will clear

the accumulator-low and are sign- extended. An exception is mov direct address,

axh [eu], when moving data into accumulator-high can be controlled with sign exten-

sion or with sign extension unaffected (the accumulator extension aXe is

unaffected).

In all arithmetic operations between 16-bit registers and aX (36 bits), the 16-bit

extension in the MSBs.

It is recommended that the flags are used immediately after the instruction that

updated them. Otherwise, very careful programming is required (some flags may

be changed in the meantime).

The condition field is almost always an optional field, except when the condition

is followed by another optional field as in reti instruction. The condition field is the

last field of the instruction. When the condition field is missing, the condition is

true.

Examples:

shr4 true is the same as shr4, but in reti true, context the true cannot be

omitted.

10. General Restrictions:

a) Arithmetic and logical operations (but not bit-manipulation operations) must not

be performed with the same accumulator as the source (soperand) and the destina-

tion (doperand).

Example: add a0, a0 is not allowed (shfc a0, a0 is allowed)

b) An instruction immediately following an instruction that modifies the rb register

may not use the index addressing mode. The only exception is when rb is modified

using a long immediate operand (mov ## long immediate, rb).

11. Two nop instructions should follow instructions that use the pc as a destination

AT75C Datasheet(PDF) 35 Page - ATMEL Corporation