ACS8520T Semtech, ACS8520T Datasheet - Page 90

• Manufacturer Part Number: ACS8520T
• Description: Synchronous Equipment Timing Source (SETS) for Stratum 3/4E/4 and SMC Systems
• Manufacturer: Semtech

Address (hex):
Address (hex):
Revision 3.02/October 2005 © Semtech Corp.
ADVANCED COMMUNICATIONS
Register Name
Register Name
auto_averaging fast_averaging
Bit No.
Bit No.
Bit 7
[7:0]
Bit 7
7
6
3F
40
cnfg_holdover_frequency
[15:8]
Description
holdover_frequency_value[15:8]
This value in this register is combined with the value
in Reg. 3E and Bits [2:0] of Reg. 40 to represent the
programmed Holdover frequency of the T0 DPLL.
This register is designed such that software can
read the sts_current_DPLL_frequency register
(Reg. 0C, Reg. 0D and Reg. 07) and filter the value.
The result will then be in a suitable format to simply
write back to the cnfg_holdover_frequency register.
*This register can be programmed to read back the
internally averaged Holdover frequency rather than
the programmed value, see Bit 5 of Reg. 40
cnfg_holdover_modes.
cnfg_holdover_modes
Description
auto_averaging
Bit to enable the use of the averaged frequency
value during Holdover. This bit is overridden by the
manual Holdover control (Bit 4, man_holdover, in
Reg. 34).
fast_averaging
Bit to control the rate of averaging of the Holdover
frequency. Fast averaging gives a -3db response
point of approximately 8 minutes. Slow averaging
give a -3db response point of approximately 110
minutes.
Bit 6
Bit 6
read_average
Bit 5
Bit 5
Description
Description
holdover_frequency_value[15:8]
Bit 4
Bit 4
mini_holdover_mode
FINAL
Page 90
(R/W) Bits [15:8] of the manual
Holdover frequency register.
(R/W) Register to control the
Holdover modes of the T0 DPLL.
Bit Value
Bit Value
Bit 3
Bit 3
0
1
0
1
-
Value Description
In order to calculate the Holdover ppm offset of the
DPLL with respect to the crystal oscillator frequency,
the value in Reg. 3E hex and Bits [2:0] of Reg. 40
need to be concatenated. This value is a 2’s
complement signed integer. The value multiplied by
0.0003068 dec will give the value in ppm.
Value Description
Averaged frequency not used, Holdover frequency
either manual or instantaneously frozen.
Averaged frequency used, providing manual
Holdover mode is not engaged.
Slow Holdover frequency averaging enabled.
Fast Holdover frequency averaging enabled.
Bit 2
Bit 2
holdover_frequency_value [18:16]
Default Value
Default Value
ACS8520 SETS
Bit 1
Bit 1
DATASHEET
www.semtech.com
0000 0000
1000 1000
Bit 0
Bit 0