Texas Instruments MSP50C6xx Class 1 Instruction Encoding, Class 1a Instruction Description, C1b

Instruction Classification

Class 1a provides the four basic instructions of load, store, add, and subtract between accumulator and data memory. Either the accumulator or the offset accumulator (A~ bit dependent) can be stored in memory with the MOV instruction. The MOV instruction can load the accumulator (or its offset) depending on the ~A bit. The ADD or SUB instructions add or subtract memory from an accumulator register and save the results in the accumulator register (~A=0) or its offset (~A=1). Two of the four codes provided by the next A field will cause a pre–increment or a predecrement of the accumulator register pointer (AP) prior to execution. This preincrement is a permanent change to the referenced AP and further expands the use of the accumulator block as an efficient workspace. Preincrements and predecrements are not available in string mode

One of the four codes of the An field (An = 11 binary) will cause the instruction to be treated as a multicycle string instruction. This will not result in any perma- nent modification to the referenced AP.

Since there is no reference to offset accumulators in Class 1b instructions, the execution operates on memory and accumulators. All other modes of control (string, preincrement/predecrement AP, data memory addressing modes, etc.) are provided for logical, byte, multiply-accumulate, and barrel shift instructions.

Table 4–13. Class 1 Instruction Encoding

Bit	16	15	14	13		12	11	10	9	8	7	6	5	4	3	2	1	0
Class 1a	0	0	C1a			~A~	next A		An					adrs
Class 1b	0	1			C1b			s	An					adrs

Table 4–14. Class 1a Instruction Description

C1a		Mnemonic	Description
0	0	ADD An[~], An, {adrs} [, next A]	Add contents of data memory location referred by {adrs} to accumulator An
		ADDS An[~], An, {adrs}	and store the results in the same accumulator An (if ~A=0) or offset
			accumulator An~ (~A=1). ALU status is modified.
0	1	SUB An[~], An, {adrs} [, next A]	Subtract contents of data memory location referred by {adrs} from
		SUBS An[~], An, {adrs}	accumulator An and store the results in the same accumulator An (if ~A=0)
			or offset accumulator An~ (~A=1). ALU status is modified.
1	0	MOV An[~], {adrs} [, next A]	Load accumulator An (~A=0) or offset accumulator An~ (~A=1) from data
		MOVS An[~], {adrs}	memory location referred to {adrs}. ALU status is modified.
1	1	MOV {adrs}, An[~] [, next A]	Store accumulator (A~=0) or offset accumulator (A~=1) to data memory
		MOVS {adrs}, An[~]	location referred to by addressing mode {adrs}. Transfer status is modified.

4-26