UPD17708 datasheet(59/356 Pages) NEC

59 / 356 page

µPD17704, 17705, 17707, 17708, 17709

7.2 Configuration and Function of Each Block

7.2.1 ALU

The ALU performs arithmetic operation, logical operation, bit judgment, comparison, rotation, and transfer

of 4-bit data according to instructions specified by the program.

7.2.2 Temporay registers A and B

Temporary registers A and B temporarily store 4-bit data.

These registers are automatically used when an instruction is executed, and cannot be controlled by program.

7.2.3 Program status word

The program status word controls the operation of and stores the status of the ALU.

For further information on the program status word, also refer to 5.8 Program Status Word (PSWORD).

7.2.4 Decimal adjustment circuit

The decimal adjustment circuit converts the result of an arithmetic operation into a decimal number if the BCD

flag of the program status word is set to “1” during arthmetic operations.

7.2.5 Address control circuit

The address control circuit specifies an address of the data memory.

At this time, address modification by the index register and data memory row address pointer is also

controlled.

7.3 ALU Processing Instruction List

Table 7-1 lists the ALU operations when each instruction is executed.

Table 7-2 shows how data memory addresses are modified by the index register and data memory row

address pointer.

Table 7-3 shows decimal adjustment data when a decimal operation is performed.

UPD17708 Datasheet(PDF) 59 Page - NEC