ds3104-se Maxim Integrated Products, Inc., ds3104-se Datasheet - Page 51

• Manufacturer Part Number: ds3104-se
• Description: Line Card Timing Ic With Synchronous Ethernet Support
• Manufacturer: Maxim Integrated Products, Inc.

________________________________________________________________________________________ DS3104-SE
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 which 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. 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 Considerat ions
Due to the dual-power-supply nature of the DS3104-SE, 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
less than one parasitic diode drop below the 1.8V supply. The second method is to ramp up the 3.3V 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 DS3104-SE to tune it for optimal performance. This
series of writes is called the initialization script. Each die revision of the DS3104-SE has a different initialization
script. Download the latest initialization scripts from the DS3104-SE web page at www.maxim-ic.com/DS3104-SE,
or email [e-mail].
51