Texas Instruments MSP50C614 - Manual (Page 96)

System Registers
4-4
It is recommended to avoid using the TOS register altogether in applications
and leave its operation to development tools only.
4.2.6 Product High Register (PH)
This register holds the upper 16 bits of the 32 bit result of a multiplication,
multiply-accumulate, or shift operation. The lower 16 bits of the result are
stored in the PL register. The PH register can be loaded directly by MOV
instructions. Special move accumulate instructions MOVAPH, MOVAPHS,
MOVSPH, MOVSPHS also use the PH register.
4.2.7 Product Low Register (PL)
This register holds the lower 16 bits of the 32 bit result of a multiplication,
multiply-accumulate, or shift operation. The upper 16 bits of the result are
stored in the PH register. There are no instructions that load or save the PL
register directly, but multiply-accumulate instructions allow the contents of the
PL register to be added, subtracted or transferred to the accumulator.
4.2.8 Accumulators (AC0–AC31)
There are 32 accumulators on the MSP50P614/MSP50C614. Each is 16 bits
wide. The first sixteen accumulators, AC0–AC15, have offset accumulators,
AC16–AC31, and vice versa. At any one time, four accumulators can be
selected through accumulator pointer registers, AP0–AP3 (see section 4.2.9).
Some instructions can specify offset accumulators which are the
accumulators pointed to by AP
n +16 or APn –16 (whichever is in the range 0
to 31). The offset accumulators are indicated by an offset bit (A~) in some
instructions. When this bit is 0, A
n points to the accumulator directly. If it is 1,
then A n~ points to the offset (for some instructions this scheme changes). The
selected accumulator pointer register should contain the index to the
corresponding accumulator. For example, if AP0 has a value of 25, then it is
pointing to accumulator AC25. If the offset bit is 1, A0~, then it is pointing to
accumulator AC9 (25–16=9). Because, accumulators can only be addressed
through accumulator pointers, special symbols are used in MSP50P614/
MSP50C614 instructions. Accumulators are indicated by the symbol A
n,
where n ranges from 0 to 3. The symbol indicates that the accumulator pointed
to by AP n is the referring accumulator. If APn has a value of k, it is pointing to
accumulator AC k. Similarly, An~ points to the offset accumulator pointed by
AP n. For example, if AP3 = 22, then A3 is accumulator AC22 and A3~ is
accumulator AC6.