UPD64 datasheet(22/68 Pages) NEC

22 / 68 page

µPD63, 63A, 64

5. STANDBY FUNCTION

5.1 Outline of Standby Function

To save current consumption, two types of standby modes, i.e., HALT mode and STOP mode, are made available.

In STOP mode, the system clock stops oscillation. At this time, the XIN and XOUT pins are fixed at a low level.

In HALT mode, CPU operation halts, while the system clock continues oscillation. When in HALT mode, the

timer (including REM output and LED output) operates.

In either STOP mode or HALT mode, the statuses of the data memory, accumulator, and port register, etc.

immediately before the standby mode is set are retained. Therefore, make sure to set the port status for the system

so that the current consumption of the whole system is suppressed before the standby mode is set.

Table 5-1. Statuses During Standby Mode

STOP Mode

HALT Mode

Setting instruction

HALT instruction

Clock oscillation circuit

Oscillation stopped

Oscillation continued

CPU

• Operation halted

Data memory

• Immediately preceding status retained

Operation

Accumulator

• Immediately preceding status retained

statuses

Flag

• 0 (When 1, the flag is not placed in the standby mode.)

• Immediately preceding status retained

Port register

• Immediately preceding status retained

Timer

• Operation halted

• Operable

(The count value is reset to “0”)

Cautions 1. Write the NOP instruction as the first instruction after STOP mode is canceled.

2. When standby mode is canceled, the status flag (F) is set (to 1).

3. If, at the point the standby mode has been set, its cancelation condition is met, then the

system is not placed in the standby mode. However, the status flag (F) is set (1).

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