SM34 Data Sheet #:

TM095

Page 10

Rev:

05 Date: 11/19/12

© Copyright 2012 The Connor-Winfield Corp. All Rights Reserved

Specifications subject to change without notice

Reference Input Quality Monitoring

Each reference input is monitored for signal presence and frequency offset. Signal presence for the

Ref1-8 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

Ref1-8 inputs and the calibrated local oscillator is available in the Ref_Frq_Offset registers (8). Register Ref_

Pullin_Sts indicates, for each of the Ref1-8 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 Ref1-8

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 eight reference input signals (

Ref 1-8) are selected for synchronization in Master mode (as below in the Op_Mode register

description. 0x05).

Ref 1-8 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 and the detected frequency can be read from the

Ref_Frq_Priority registers (See

Register Descriptions and Operation section).

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.

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.

In automatic mode, the reference is selected according to the priorities written to the eight

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).

Detailed Description continued

Serial Bus Timing

Table 4

Symbol

Parameter

Minimum

Nominal

Maximum

Units

Notes

t

SPI_EnablelowtoSPI_CLKlow

15

-

-

ns

t

SPI_CLKhightime

25

-

-

ns

t

SPI_CLKlowtime

25

-

-

ns

t

Read/Writesetuptime

15

-

-

ns

t

Read/Writeholdtime

15

-

-

ns

t

Dataready

-

-

25

ns

t

DataHold

15

-

-

ns

t

ChipSelecttodatatri-state

5

-

-

ns

t

Minimumdelaybetweensuccessiveaccesses 300

-

-

ns