STC3500 Datasheet, PDF (39/48 Pages) Connor-Winfield Corporation – INTEGRATED - STRATUM 3 TIMING SOURCE

Application Notes continued
Control Modes
The STC3500 device may be controlled and interfaced in a pure hardware mode with pin signals, or via SPI or parallel
bus/register access. With register access, the device can in turn be operated in a manual control mode, or automatic
control and reference selection mode. Hardware mode is most suitable for simple environments where minimal external
intelligence is desired. Register access provides more detailed visibility and control for references and general
synchronization operation. These three main operating environments are detailed as follows:
Hardware Control Interfaces
Figure 12
Reset
BITS output
frequency select
Reset
BITS_Sel
STC3500
Inputs
Master/Slave
Vdd3.3
Reference/
Operational
Mode Select
M/S
HM_Ref
Sel0
Sel1
Sel2
Sel3
LOS
LOL
Hold_Avail
Outputs
Hardware Control – The device interfaces for hardware control are shown in Figure 12.
Reset may be pulled low for a minimum of 100nS during chip start-up (or any other desired time) to initialize the full
device state. However, power-up will also perform a reset, so in a minimal configuration, Reset may be tied input high.
The BITS clock output frequency is selected by the BITS_Sel pin. When BITS_Sel = 1, the BITS frequency is 1.544
MHz, and when BITS_Sel = 0, the BITS frequency is 2.048 MHz.
M/S - Determines the master or slave mode. Set to “1” for a master, and “0” for a slave. Master/slave switches should
be performed with minimal delay between switching the states of each of the two devices. This can be easily
accomplished, for example, by controlling the master/slave state with a single signal, coupled to one of the devices
through an inverter.
For simplex operation, the device should be in Master mode - set M/S to “1”.
HM_Ref - Set to “1” for hardware control of reference selection and operational mode.
Preliminary Data Sheet: TM060 Page 39 of 48 Rev: P06 Date: 11/22/04
© Copyright 2001 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice