SM3G Datasheet, PDF (9/36 Pages) Connor-Winfield Corporation – ULTRA MINIATURE STRATUM 3 MODULE

Detailed Description continued
Table 4
Serial Interface Timing
Symbol Parameter
Minimum
Nominal Maximum Units
t_CS
SPI_Enable low to SPI_CLK low
15
-
-
ns
t_CH
SPI_CLK high time
25
-
-
ns
t_CL
SPI_CLK low time
25
-
-
ns
t_RWs
Read/Write setup time
15
-
-
ns
t_RWh
Read/Write hold time
15
-
-
ns
t_DRDY
Data ready
-
-
25
ns
t_HLD
Data Hold
15
-
-
ns
t_CSTRI
Chip Select to data tri-state
5
-
-
ns
t_CSMIN
Minimum delay between successive accesses 300
-
-
ns
Note: The SPI port should not be accessed until 1200ms after reset has transitioned from low to a high state.
Notes
Reference Input Quality Monitoring
Each reference input is monitored for signal presence and frequency offset. Signal presence for the Ref1-4 inputs is indicated in
the Ref_Activity register and signal presence for the M/S REF is indicated in bit 0 of the M/S REF_Activity register. The frequency
offset between the Ref1-4 inputs and the calibrated local oscillator is available in the Ref_Frq_Offset registers (4). Register Ref_
Pullin_Sts indicates, for each of the Ref1-4 inputs, if the reference is within the maximum pull-in range. The maximum pull-in range
is indicated in register Max_Pullin_Range, and may be set in 0.1ppm increments. Typically, it would be set according to the values
specified by the standards (GR-1244) appropriate for the particular stratum of operation.
The Ref_Qualified register contains the “anded” condition of the Ref_Activity and Ref_Pullin_Sts registers for each of the Ref1-4
inputs, qualified for 10 seconds. When a reference signal has been present for > 10 seconds and is within the pull-in range, it’s bit is
set.
The Ref_Available register contains the “anded” condition of the Ref_Qualified register and the Ref_Mask register, and therefore
represents the availability of a reference for selection when automatic reference and operational mode selection is enabled.
Reference Input Selection, Frequencies, and Mode Selection
One of four reference input signals (Ref 1-4) are selected for synchronization in Master mode (as below in the Op_Mode register
description. 0x05).Ref1-4 may each be 8 kHz, 1.544 MHz, 2.048 MHz, 12.96 MHz, 19.44 MHz, 25.92 MHz, 38.88 MHz, 51.84 MHz
or 77.76 MHz.
Reference frequencies are auto-detected (frequency determined by the chip) and the detected frequency can be read from the
Ref_Frq_Priority registers (See Register Descriptions and Operation section).
The M/S REF input for slave operation is frequency auto-detected and may be 8kHz, 1.544MHz, 2.048MHz, 12.96MHz, 19.44MHz,
25.92MHz, 38.88MHz, 51.84MHz or 77.76MHz. Signal presence and frequency for the M/S REF input is indicated in bits 0-3 of the
M/S REF_Activity register.
Active reference and operational mode selection may be manual or automatic, as determined by bit 1 in the Ctl_Mode register. In
manual mode, register writes to Op_Mode select the reference and mode. The reset default is manual mode.
In automatic mode, the reference is selected according to the priorities written to the four Ref_Frq_Priority registers. Individual
references may be masked for use/non-use according to the Ref_Mask register. A reference may only be selected if it is “available”
- that is, it is qualified, as indicated in the Ref_Qualified register, and is not masked (See Reference Input Quality Monitoring and
Register Descriptions and Operation sections).
Furthermore, Bit 3 of each Ref_Frq_Priority register will determine if that reference is revertive or non-revertive. When a reference
fails, the next highest priority “available” (signal present, non-masked, and acceptable frequency offset) reference will be selected.
When a reference returns, it will be switched to only if it is of higher priority and the current active reference is marked “Revertive”.
Additionally, the reversion is delayed according to the value written to the Ref_Rev_Delay register (From 0 to 255 minutes).
SM3G5 Data Sheet #: TM083 Page 9 of 36 Rev: 05 Date: 01/26/11
© Copyright 2011 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice