ACS8520T Semtech, ACS8520T Datasheet - Page 89

• 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
Bit No.
Bit No.
Bit 7
[7:0]
Bit 7
[7:0]
3D
3E
cnfg_nominal_frequency
[15:8]
Description
cnfg_nominal_frequency_value[15:8]
This register is used in conjunction with Reg. 3C
(cnfg_nominal_frequency_value[7:0]) to be able to
offset the frequency of the crystal oscillator by up to
+514 ppm and –771 ppm. The default value
represents 0 ppm offset from 12.800 MHz.
This value is an unsigned integer.
The value in Reg. 3C/3D is used within the DPLL to
offset the frequency value used in the DPLL only.
This means that the value programmed will affect
the value reported in the
sts_current_DPLL_frequency (Reg 07/0D/0C). It
will also affect the value programmed into
holdover_frequency_value in the
cnfg_holdover_frequency register (Reg 3E/3F/40)
and the DPLL frequency offset limit programmed
into the cnfg_DPLL_freq_limit (Reg 41/42). It must
be noted, however, that this “calibrated” frequency
is NOT used in the frequency monitors affecting
Regs 49, 4A, 4C & 4D. These registers
(cnfg_freq_mon_threshold,
cnfg_current_freq_mon_ threshold,
sts_freq_measurement, cnfg_DPLL_soft_limit)
which all use the uncalibrated crystal frequency.
The frequency monitors can also use the clock from
the output of the DPLL by programming bit
freq_mon_clock in cnfg_monitors (Reg 48).
cnfg_holdover_frequency
[7:0]
Description
holdover_frequency_value[7:0]
Bit 6
Bit 6
Bit 5
Bit 5
cnfg_nominal_frequency_value[15:8]
Description
Description
holdover_frequency_value[7:0]
Bit 4
Bit 4
FINAL
Page 89
(R/W) Bits [15:8] of the register
used to calibrate the crystal
oscillator used to clock the
device.
(R/W) Bits [7:0] of the manual
Holdover frequency register.
Bit Value
Bit Value
Bit 3
Bit 3
-
-
Value Description
In order to program the ppm offset of the crystal
oscillator frequency, the value in Reg. 3C and
Reg. 3D hex need to be concatenated. This value is
an unsigned integer. The value multiplied by
0.0196229 dec will give the value in ppm. To
calculate the absolute value, the default (39321)
needs to be subtracted.
Value Description
See Reg. 3F (cnfg_holdover_frequency) for details.
Bit 2
Bit 2
Default Value
Default Value
ACS8520 SETS
Bit 1
Bit 1
DATASHEET
www.semtech.com
1001 1001
0000 0000
Bit 0
Bit 0