AMD
TAXI Technical Information Publication #89-04
S u b je c t : TAXI P LL Lo c k -Up Du rin g P o w e r-On !
Qu e s t io n :
Is there a recommended power-on sequence for the TAXIchips to prevent PLL lock-up?
An s w e r:
Early versions of the -70 TAXIchips did have some sensitivities associated with hot-
plug-in lock-up, fast VCC rise time, and/or power supply sequencing during power-on
causing occasional PLL lock-up. These potential problems were addressed in the -125
TAXIchips with an improved circuit design. The -125 TAXIchips do not exhibit any
known power-on problems, but a PLL Reset function is available on a package pin and
may be used to restart the PLL if problems occur.
Use of the external PLL Reset pin should not be necessary with the -125 TAXIchips, but
there may be specific situations where its use may be helpful with the TAXI Receiver.
There are possible situations where large amounts of noise may occur on the Receiver
serial data inputs. Under these conditions the Rx-PLL may attempt to track the noise to
an indeterminate frequency. This deviation in frequency may adversely affect data
recovery when a good data stream reappears. System requirements may also place a
restriction on the allowed clock frequency deviation. Use of the PLL Reset function on
the Receiver may assist in the containment of some of these effects.
All VCCs may be powered-on simultaneously with a common supply. It is only recom-
mended that the TAXI GND pins be connected to a common Ground and the VCC pins
be separately filtered and decoupled to that Ground. Variations in power-on times due to
separate VCC filtering and decoupling are not a problem. Use of a common VCC supply is
sufficient as long as noise filtering of the supply at the TAXI VCC pins is adequate,
therefore use of separate power supplies for the VCCs is usually not necessary.
Refer to Section 6.1, for more information concerning power supply layout and decoupling. Further
information is also available in TAXI TIP #89-02, TAXI Receiver RESET Pin Function.
98
TAXIchip Integrated Circuits Technical Manual
AMD [ AMD ]
