Register Controlling Clock Generation Circuit - NEC mPD789026 Subseries User Manual

5.3 Register Controlling Clock Generation Circuit

The clock generation circuit is controlled by the following register:
• Processor clock control register (PCC)
(1) Processor clock control register (PCC)
PCC sets CPU clock selection and the ratio of division.
PCC is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets PCC to 02H.
Symbol 7 6
PCC 0 0
PCC1
µ
0
f (0.2 s)
X
µ
1 f /2 2 (0.8 s)
X
Caution Be sure to set bit 0 and bits 2 to 7 to 0.
Remarks 1. f : System clock oscillation frequency
X
2. The parenthesized values apply to opration at f
3. Minimum instruction execution time: 2 f
• When f
• When f
86
CHAPTER 5 CLOCK GENERATION CIRCUIT
Figure 5-2. Processor Clock Control Register Format
5 4 3
0 0 0
CPU Clock (f
= 0.2 µ s : 0.4 µ s
CPU
= 0.8 µ s : 1.6 µ s
CPU
User's Manual U11919EJ3V0UM00
2 1 0 Address
0 PCC1 0
) Selection
CPU
= 5.0 MHz.
X
CPU
After Reset R/W
FFFBH 02H R/W