M30240ECFP MITSUBISHI [Mitsubishi Electric Semiconductor], M30240ECFP Datasheet - Page 41

• Manufacturer Part Number: M30240ECFP
• Description: M30240 Group Specification
• Manufacturer: MITSUBISHI [Mitsubishi Electric Semiconductor]

Specifications in this manual are tentative and subject to change
Frequency Synthesizer Circuit
2.17 Frequency Synthesizer Circuit
Figure 1.23: Frequency Synthesizer Circuit
Figure 1.24: Frequency Synthesizer Prescaler Register (FSP)
2.17.1 Prescaler
The Frequency Synthesizer Circuit generates a 48MHz clock needed by the USB block and a clock f
that are both a multiple of the external input reference clock f(Xin). A block diagram of the circuit is shown
in Figure 1.23.
The frequency synthesizer consists of a prescaler, frequency multiplier macro, a frequency divider
macro, and five registers, namely FSP, FSM, FSC, FSD, and FSCCR. Clock f(Xin) is prescaled down
using FSP to generate f
using FSD to produce the clock f
and sent out of the frequency synthesizer block as signal f
Clock f
and the clock input to the prescaler f(Xin) is as follows:
• f
• Note: f(Xin) frequency below 1 MHz is not recommended.
Setting FSP to 255 disables the prescaler and f
PIN
= f(Xin) / 2(n+1) where n is a decimal number between 0 and 254.
PIN
is a divided down version of clock f(Xin) (see Figure 1.24). The relationship between f
f(Xin)
MSB
7
03DE
Prescaler
Bit 7
FSP
PIN
. f
12 MHz
1 MHz
2 MHz
3 MHz
6 MHz
Bit 6
f
PIN
PIN
03DD
f
PIN
is multiplied using FSM to generate an f
FSM
SYN
Frequency
Multiplier
Bit 5
. The f
f(Xin)/2(n+1) = f
255
5
2
1
0
2
Dec(n)
1-41
VCO
Bit 4
03DC
FSP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
clock is optimized for 48 MHz operation and is buffered
f
LS
VCO
FSC
FF
05
02
01
00
PIN
Hex(n)
PIN
Bit 3
= f(Xin).
USB
12.00 MHz
12.00 MHz
12.00 MHz
12.00 MHz
12.00 MHz
Frequency
Divider
Bit 2
. This signal is used by the USB block.
03DF
USBC5
f(Xin)
EN
FSD
8 Bit
Bit 1
f
f
SYN
Data Bus
USB
VCO
Mitsubishi microcomputers
03DB
M30240 Group
FSCCR
clock which is then divided
Bit 0
FSCCR0
LSB
0
Address: 03DE
Access: R/W
Reset:
FF
16
16
SYN
PIN