AM7968-125DKC Advanced Micro Devices, AM7968-125DKC Datasheet - Page 100

• Manufacturer Part Number: AM7968-125DKC
• Description: TAXIchip Integrated Circuits(Transparent Asynchronous Xmitter-Receiver Interface)
• Manufacturer: Advanced Micro Devices

AMD
TAXI Technical Information Publication #89-02
Subject: TAXlchip RESET Pin Function
Question:
How long must the RESET pin be held low in order to insure that the TAXIchip has
reset?
Answer:
The RESET pin is level sensitive and after a LOW input level is asserted it instantane-
ously forces the Phase Lock Loop (PLL) to its lowest possible frequency (approximately
5 to 10 MHz). A 1 ms LOW pulse should allow sufficient time for the PLL to reach a
stable state. Preliminary tests conducted in the lab reported that for the full TAXI
frequency and temperature range, the time required to recover from a reset was less
than 100 s.
Resetting is intended to allow graceful recovery from the rare occurrence of a PLL
lock-up due to noise bursts on the serial data lines, as may occur when light is removed
from certain optical links. In a fiber-optic coupled system, loss of optical signal may
cause the optical receiver to oscillate, causing the TAXI Receiver to track the oscillation
to an indeterminate frequency. Care must be taken to avoid the oscillation, or a reset
can be used to recover from it. After reset, the PLL begins tracking incoming data, and
the byte boundary remains undefined until the transmitted data includes a Sync (JK).
The Sync is a unique bit pattern which forces the TAXI Receiver to align itself to the
correct byte boundary.
In a coaxial system when a loss of incoming signal drive occurs, there will be no data for
the TAXI Receiver to track. This quiet state will be interpreted as a continuous data
pattern. The Receiver decodes this Quiet-Line-State differently depending upon the
operational mode selected: 8-bit, 9-bit, or 10-bit. In 8-bit mode the TAXI Receiver will
generate continuous CSTRBs with command outputs all high ( F Hex ). In 9-bit or 10-bit
modes there is no defined interpretation of an incoming quiet data stream thus generat-
ing continuous CSTRBs and forcing the violation output (VLIN) to be continuously high.
Further information on the effects of incoming signal drive loss is available in TAXI TIP
#89-01, Receiver Response to Loss of Input Signal.
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TAXIchip Integrated Circuits Technical Manual