ds3102 Maxim Integrated Products, Inc., ds3102 Datasheet - Page 52

• Manufacturer Part Number: ds3102
• Description: Stratum 3 Timing Card Ic With Synchronous Ethernet Support
• Manufacturer: Maxim Integrated Products, Inc.

____________________________________________________________________________________________ DS3102
7.11 Reset Logic
The device has three reset controls: the RST pin, the RST bit in MCR1, and the JTAG reset pin JTRST. The RST
pin asynchronously resets the entire device, except for the JTAG logic. When the RST pin is low all internal
registers are reset to their default values, including those fields that latch their default values from, or based on, the
states of configuration input pins when the RST goes high. The RST pin must be asserted once after power-up
while the external oscillator is stabilizing.
The MCR1:RST bit resets the entire device (except for the microprocessor interface, the JTAG logic, and the RST
bit itself), but when RST is active, the register fields with pin-programmed defaults do not latch their values from, or
based on, the corresponding input pins. Instead, these fields are reset to the default values that were latched when
the RST pin was last active.
Maxim recommends holding RST low while the external oscillator starts up and stabilizes. Some OCXOs take
250ms or more to start up and stabilize their output signals to valid logic levels and pulse widths. An incorrect reset
condition could result if RST is released before the oscillator has started up completely.
Important: System software must wait at least 100µs after reset (RST pin or RST bit) is deasserted before
initializing the device as described in Section 7.13.
7.12 Power-Supply Considerations
Due to the dual-power-supply nature of the DS3102, some I/Os have parasitic diodes between a 1.8V supply and a
3.3V supply. When ramping power supplies up or down, care must be taken to avoid forward-biasing these diodes
because it could cause latchup. Two methods are available to prevent this. The first method is to place a Schottky
diode external to the device between the 1.8V supply and the 3.3V supply to force the 3.3V supply to be within one
- ∼0.4V). The second method is to ramp up the 3.3V
parasitic diode drop below the 1.8V supply (i.e., V
> V
DDIO
DD
supply first and then ramp up the 1.8V supply.
7.13 Initialization
After power-up or reset, a series of writes must be done to the DS3102 to tune it for optimal performance. This
series of writes is called the initialization script. Each DS3102 die revision has a different initialization script.
Download the latest initialization scripts from the DS3102 webpage at www.maxim-ic.com/DS3102, or email
[e-mail].
Note: System software must wait at least 100μs after reset is deasserted before initializing the device.
Rev: 012108
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