Register Controlling Clock Generator - NEC mPD789101 User Manual

CHAPTER 7 CLOCK GENERATOR ( µ PD789124, 789134 SUBSERIES)

7.3 Register Controlling Clock Generator

The clock generator is controlled by the following register:
• Processor clock control register (PCC)
(1) Processor clock control register (PCC)
PCC sets the CPU clock selection and the ratio of division.
PCC is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets the PCC to 02H.
Symbol 7 6
PCC 0 0
PCC1
0
f (0.25 s)
CC
2
1
f /2 (1.0 s)
CC
Caution Bit 0 and bits 2 to 7 must be set to 0.
Remarks 1. f : System clock oscillation frequency
CC
2. Values in parentheses are when operating at f
3. Minimum instruction execution time: 2f
• When f
• When f
96
Figure 7-2. Processor Clock Control Register Format
5 4 3 2 1
0 0 0 0 PCC1
CPU clock (f
µ
µ
= 0.25 µ s: 0.5 µ s
CPU
= 1.0 µ s: 2.0 µ s
CPU
User's Manual U13045EJ2V0UM00
0
Address After reset
0 FFFBH 02H
) selection
CPU
= 4.0 MHz.
X
CPU
R/W
R/W