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TSS461C
7
Rev. D (22 Feb 01)
6. Oscillator
An oscillator is integrated in the TSS461C, and consists of an inverting amplifier of which the input is XTAL1 and the
output XTAL2.
A parallel resonance quartz crystal or ceramic resonator must be connected to these pins. As can be seen from
Figure 3. , two capacitors have to be connected from the crystal pins to ground. The values of C1 depend on the
frequency chosen and can be selected using the nomograph given in Figure 34.
If the oscillator is not used, then a clock signal must be fed to the circuit via the XTAL1 input.
Note, that this pin will behave as a CMOS level compatible Schmitt trigger input.
In this case the XTAL2 output should be left unconnected. The oscillator also features a buffered clock output pin
CKOUT. The signal on this pin is directly buffered from the XTAL1 input, without inversion.
There is one more pin used for the oscillator. The TEST/VSS pin is in fact its ground, and unless this pin is firmly
connected to ground, with decoupling capacitors, the oscillator will not operate correctly.
The test mode itself, i.e. when the TEST/VSS pin is held high, is only intended for factory use, and the functionality
of this mode is not specified in any way.
Furthermore, it is subject to change without notice, the only exception beeing for incoming inspection tests using the
test program.
The clock signal is then fed to the clock generator that generates all the necessary timing signals for the operation of
the circuit. The clock generator is controlled by a 4-bit code called the clock divider.
f
(TSCLK)
f
(XTAL1)
n
16
Table 2. Clock Divider.
32 MHz
24 MHz
16 MHz
Clock
Divider
Divide
by
Ktimes
lot
/s
Kbits
/s
Ktimes
lot
/s
Kbits
/s
Ktimes
lot
/s
Kbits
/s
0000
1
1000
800
0001
2
1000
800
750
600
500
400
0010
4
500
400
375
300
250
200
0011
8
250
200
187.5
150
125
100
0100
16
125
100
93.75
75
62.50
50
0101
32
62.5
50
46.875
37.5
31.25
25
0110
64
31.25
25
23.438
18.75
15.625
12.5
0111
128
15.625
12.5
11.718
9.375
7.813
6.25
1000
1.5
1333
1067
1000
800
666.667
533.333
1001
3
666.667
533.333
500
400
333.333
266.666
1010
6
333.333
266.666
250
200
166.666
133.333
1011
12
166.666
133.333
125
100
83.333
66.666
1100
24
83.333
66.666
62.5
50
41.666
33.333
1101
48
41.666
33.333
31.25
25
20.833
16.666
1110
96
20.833
16.666
15.625
12.5
10.416
8.333
1111
192
10.416
8.333
7.813
6.125
5.208
4.166