Texas Instruments MSP50C6xx manual Product High Register PH, Product Low Register PL

System Registers

It is recommended to avoid using the TOS register altogether in applications and leave its operation to development tools only.

4.2.6Product 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.

4.2.7Product 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.

4.2.8Accumulators (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 APn +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, An points to the accumulator directly. If it is 1, then An~ 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 An, where n ranges from 0 to 3. The symbol indicates that the accumulator pointed to by APn is the referring accumulator. If APn has a value of k, it is pointing to accumulator ACk. Similarly, An~ points to the offset accumulator pointed by APn. For example, if AP3 = 22, then A3 is accumulator AC22 and A3~ is accumulator AC6.

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