DS4000 Dallas Semiconducotr, DS4000 Datasheet - Page 8

• Manufacturer Part Number: DS4000
• Description: Digitally Controlled TCXO
• Manufacturer: Dallas Semiconducotr

DIGITAL TUNING THE BASE CRYSTAL FREQUENCY
When using the 2-wire interface for tuning the base frequency, the frequency tuning register is used. The frequency
tuning register contains two’s complement data. The data is used to add or subtract an offset from the crystal
loading register. When the tuning register is programmed with a value, the next temperature-update cycle sums the
programmed value with the factory-compensated value. This allows the user/system to digitally control the base
frequency by a microcontroller using the 2-wire protocol.
FREQUENCY TUNING REGISTER (66h)
FOS[6:0], Frequency Offset: These bits are used to tune the base crystal frequency. Each bit represents
approximately 0.08ppm and, therefore, for a value of 07FH, pushes or pulls the base frequency by approximately
10.16ppm.
SIGN, Sign Bit: This bit is used to determine whether to add or subtract the frequency offset from the crystal
loading.
Table 1. Frequency Tuning Relationship
Bit
Name
Default
FREQUENCY OFFSET
CALCULATED
+10.16
-10.16
(ppm)
+0.08
+1.84
+5.28
+8.00
-8.00
-5.28
-1.84
-0.08
0.0
SIGN
7
0
FO6
6
0
DIGITAL DATA
0111 1111
0110 0100
0100 0010
0001 0111
0000 0001
0000 0000
1111 1111
1110 1000
1011 0011
1001 1100
1000 0000
(Binary)
FO5
5
0
8 of 16
FO4
4
0
DIGITAL DATA
(hex)
9Ch
7Fh
FFh
E8h
B3h
64h
42h
17h
01h
00h
80h
FO3
3
0
FO2
2
0
FO1
1
0
FO0
0
0