- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
206
ECK-28MHz INT / ECK-27MHz LL Switching System (automatic setting)
This system uses an external circuit to detect the presence or absence of external VD input, and switches
between LL and INT automatically. INT mode operates with 28MHz ECK input. LL mode uses 27MHz ECK
input. Switching between INT and LL is handled automatically by an external VD detection circuit.
A block diagram of the system is shown in
SYSSELFLG is assigned to a port in advance. See
for information on SYSSELFLG and the parameter settings that are switched according to the
SYSSELFLG value.
When switching from INT to LL (when there is external VD input), the following operations are performed.
• SYSSELFLG, which is assigned to a specified port, is set to 1[h] to switch MODESEL/SGMODE to the LL setting.
• The MCK switching circuit is switched to the VCO position (MCK clock supply).
• The ECK switching circuit is switched to the 27MHz position (ECK 27MHz clock supply).
When switching from LL to INT (when there is no more external VD input), the following operations are
performed.
• SYSSELFLG, which is assigned to a specified port, is set to 0[h] to switch MODESEL/SGMODE to the INT setting.
• The MCK switching circuit is switched to the GND position (MCK clock supply stopped).
• The ECK switching circuit is switched to the 28MHz position (ECK 28MHz clock supply).
Fig 12.2-15 ECK-28MHz INT/ECK-27MHz LL Switching System (automatic setting) Block Diagram
* The DIP switch is used to force-switch the system to INT mode. If it is normally left in the “H” position,
switching will be handled automatically according to whether or not there is VD input.
* Do not assign SGMODE to a port.
CXD3172AR
ESCI
MC
K
27MHz
(X'tal)
VCO
(LC)
LPF
(V-PLL)
EXT-VD
86
ESCO
87
ECK
88
PCOMP
42
43
S0
44
S1
46
EXVIDEOY
EXVIDEO
58
57
3.3V
28MHz
(X'tal)
INT mode
LL mode
Pn
*
1
SYS
SEL
F
LG
INT/LL Change signal
LL mode
INT mode
XRST
11
VD Detection
Circuit
Reset
Circuit
LL : H
INT : L
3.3V
DIPSW