HT37Q70 Holtek Semiconductor Inc., HT37Q70 Datasheet - Page 49

• Manufacturer Part Number: HT37Q70
• Description: 4-channel Music Synthesizer Mcu
• Manufacturer: Holtek Semiconductor Inc.

Oscillator
Various oscillator options offer the user a wide range of
functions according to their various application require-
ments. Two types of system clocks can be selected
while various clock source options for the Watchdog
Timer are provided for maximum flexibility. All oscillator
options are selected through the configuration options.
The two methods of generating the system clock are:
One of these two methods must be selected using the
configuration options.
More information regarding the oscillator is located in
Application Note HA0075E on the Holtek website.
External Crystal/Resonator Oscillator
The simple connection of a crystal across OSC1 and
OSC2 will create the necessary phase shift and feed-
back for oscillation, and will normally not require exter-
nal capacitors. However, for some crystals and most
resonator types, to ensure oscillation and accurate fre-
quency generation, it may be necessary to add two
small value external capacitors, C1 and C2. The exact
values of C1 and C2 should be selected in consultation
Rev. 1.00
External crystal/resonator oscillator
External
RC oscillator
Crystal/Resonator Oscillator
49
with the crystal or resonator manufacturer s specifica-
tion. The external parallel feedback resistor, Rp, is nor-
mally not required but in some cases may be needed to
assist with oscillation start up.
External RC Oscillator
Using the external system RC oscillator requires that a
resistor, with a value between 82k
nected between OSC1 and VSS. The generated system
clock divided by 8 will be provided on OSC2 as an output
which can be used for external synchronization pur-
poses. Note that as the OSC2 output is an NMOS
open-drain type, a pull high resistor should be connected
if it to be used to monitor the internal frequency. Although
this is a cost effective oscillator configuration, the oscilla-
tion frequency can vary with VDD, temperature and pro-
cess variations and is therefore not suitable for
applications where timing is critical or where accurate os-
cillator frequencies are required. For the value of the ex-
ternal resistor. Note that it is the only microcontroller
internal circuitry together with the external resistor, that
determine the frequency of the oscillator. The external
capacitor shown on the diagram does not influence the
frequency of oscillation.
Internal Ca, Cb, Rf Typical Values @ 5V, 25°C
7pF~9pF
Oscillator Internal Component Values
Ca
External RC Oscillator
HT37Q70/60/50/40/30/20
9pF~11pF
Cb
and 180k , is con-
February 17, 2009
300k
Rf