em6521 EM Microelectronic, em6521 Datasheet - Page 12

• Manufacturer Part Number: em6521
• Description: Mfp Version Of Em6621 Ultra Low Power Microcontroller With 4x20 Lcd Driver
• Manufacturer: EM Microelectronic

5
5.1 Oscillator
A built-in crystal oscillator generates the system operating clock for the CPU and peripheral blocks, from an
externally connected crystal (typically 32.768kHz). The oscillator circuit is supplied by the regulated voltage,
V
EM’s special design techniques guarantee the low current consumption of this oscillator. The external
impedance between the oscillator pads must be greater than 10MOhm. Connection of any other components to
the two oscillator pads must be confirmed by EM Microelectronic-Marin SA.
5.2 Prescaler
The prescaler consists of fifteen elements divider chain which delivers clock signals for the peripheral circuits
such as timer/counter, buzzer, LCD voltage multiplier, debouncer and edge detectors, as well as generating
prescaler interrupts. The input to the prescaler is the system clock signal. Power on initializes the prescaler to
Hex(0001).
Table 5.2.1 Prescaler Clock Name Definition
Table 5.2.2 Control of Prescaler Register RegPresc
With DebSel = 1 one may choose either the Ck[11] or Ck[14] debouncer frequency by selecting the
corresponding metal mask option (for ROM version only). Relative to 32kHz the corresponding max. debouncer
times are then 2 ms or 0.25 ms. For the metal mask selection refer to chapter
Switching the PrIntSel may generate an interrupt request. Avoid it with MaskIRQ32/8 = 0 selection during the
switching operation.
Copyright © 2005, EM Microelectronic-Marin SA
Bit
3
2
1
0
reg
. In sleep mode the oscillator is stopped.
System clock / 128
System clock / 32
System clock / 64
System clock/ 16
Oscillator and Prescaler
System clock / 2
System clock / 4
System clock / 8
Name
PWMOn
ResPresc
PrIntSel
DebSel
System clock
Function
R
Reset
0
0
0
0
R/W
R/W
R/W
R/W
R/W
Ck[16]
Ck[15]
Ck[14]
Ck[13]
Ck[12]
Ck[11]
Ck[10]
Name
ck [9]
Description
see 10 bit counter
Write Reset prescaler
1 -> Resets the divider chain
0 -> No action.
The Read value is always '0'
Interrupt select.
0 -> Interrupt from Ck[4]
1 -> Interrupt from Ck[6]
Debouncer clock select.
0 -> Debouncer with Ck[8]
1 -> Debouncer with Ck[11] or
Ck[14], see below
from Ck[14] down to
Ck[2], sets Ck[1].
32 KHz Xtal
32768 Hz
16384 Hz
8192 Hz
4096 Hz
2048 Hz
1024 Hz
512 Hz
256 Hz
12
System clock / 16384
System clock / 32768
System clock / 1024
System clock / 2048
System clock / 4096
System clock / 8192
System clock / 256
System clock / 512
Figure 8. Prescaler Frequency Timing
Function
Prescaler Reset
System Clock
Ck[16]
Ck[15]
Ck[14]
Ck[2]
Ck[1]
1 8.1.5.
1 1 2 H
First positive edge of 1 Hz clock is 1s after
Horizontal Scale Change
Name
Ck[8]
Ck[7]
Ck[6]
Ck[5]
Ck[4]
Ck[3]
Ck[2]
Ck[1]
www.emmicroelectronic.com
the falling reset edge
EM6521
32 KHz Xtal
128 Hz
64 Hz
32 Hz
16 Hz
8 Hz
4 Hz
2 Hz
1 Hz