NEC PD75P402 Manuale Utente Scaricare il pdf (Pagina 70)

CHAPTER 5. PERIPHERAL HARDWARE FUNCTIONS

; Assume PCC = 0011.

MOV A, #0000

0.95

s/4.19 MHz MOV PCC, A ; PCC ← 0000

BR 16 machine cycles

15.3

s/4.19 MHz

5.2.3 CPU Clock Setting

The CPU clock

is the clock supplied to the

PD75402A’s internal CPU, and the reciprocal of this clock is the

minimum instruction execution time (defined in this manual as 1 machine cycle).

On the

PD75402A,

can be switched in 3 steps by setting the PCC. In other words, with the same system clock

oscillator frequency f

XX, the minimum instruction execution time can be changed in 3 steps. By using this function

to select operation at high speed (0.95

s: When operating at 4.19 MHz) when the power supply voltage is 5 V and

low-speed operation (15.3

s: When operating at 4.19 MHz) in backup mode, applications can be implemented in

which reduced current consumption and low-power operation is possible, which is an extremely useful facility.

Fig. 5-14 Use of Variable Minimum Instruction Execution Time Function

Note As explained in the previous section,

is changed by a 4-bit memory handling instruction, but after a PCC

change, operation is at the pre-change

rate for the number of machine cycles shown in Table 5-5.

Example

0.95

s 15.3

s 0.95

➤ ➤

………… ………

5V

3V

Supply Voltage

Minimum Instruction

Execution Time

(4.19 MHz Operation)

1 2 ... 65 66 67 68 69 70 71 72 73 74 75 ... 194 195

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NEC PD75P402 Manuale Utente Pagina 70