NEC PD75P402 CPU Clock Setting, Use of Variable Minimum Instruction Execution Time Function

CHAPTER 5. PERIPHERAL HARDWARE FUNCTIONS

5.2.3CPU Clock Setting

The CPU clock Φ is the clock supplied to the μPD75402A’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 μPD75402A, Φ can be switched in 3 steps by setting the PCC. In other words, with the same system clock oscillator frequency fXX, the minimum instruction execution time can be changed in 3 steps. By using this function to select operation at high speed (0.95 μs: When operating at 4.19 MHz) when the power supply voltage is 5 V and low-speed operation (15.3 μs: 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
5V
Supply Voltage
3V
Minimum Instruction	0.95 μs	15.3 μs	0.95 μs
Execution Time
(4.19 MHz Operation)

Note As explained in the previous section, Φ is changed by a 4-bit memory handling instruction, but after a PCC change, operation is at the pre-change Φ rate for the number of machine cycles shown in Table 5-5.

Example

0.95 μs/4.19 MHz

➤

15.3 μs/4.19 MHz

……		; Assume PCC = 0011.
MOV	A, #0000
MOV	PCC, A	; PCC ← 0000
BR	16 machine cycles
…… ………

➤

59