UPD64 datasheet(12/68 Pages) NEC

12 / 68 page

µPD63, 63A, 64

2.8 Arithmetic and Logic Unit (ALU): 4 Bits

The arithmetic and logic unit (ALU), which refers to an arithmetic circuit consisting of 4 bits, executes simple

manipulations with priority given to logical operations.

2.9 Flags

2.9.1 Status flag (F)

Pin and timer statuses can be checked by executing the STTS instruction to check the status flag.

The status flag is set (to 1) in the following cases.

• If the condition specified with the operand is met when the STTS instruction has been executed

• When STANDBY mode is canceled.

• When the cancelation condition is met at the point of executing the HALT instruction. (In this case, the system

is not placed in STANDBY mode.)

Conversely, the status flag is cleared (to 0) in the following cases:

• If the condition specified with the operand is not met when the STTS instruction has been executed.

• When the status flag has been set (to 1), the HALT instruction executed, but the cancelation condition is not

met at the point of executing the HALT instruction. (In this case, the system is not placed in STANDBY mode.)

Table 2-1. Conditions for Status Flag (F) to be Set by STTS Instruction

Operand Value of STTS Instruction

Condition for Status Flag (F) to be Set

0000

High level is input to at least one of KI pins.

The down counter of the timer is 0.

Either of the combinations

[The following condition is added in addition to the above.]

of b2, b1, and b0 above.

High level is input to at least one of S0 and S1 pins.

UPD64 Scheda tecnica(PDF) 12 Page - NEC