Browse Prior Art Database

Technique for Detecting Noise on the JTAG Bus Test Clock

IP.com Disclosure Number: IPCOM000115858D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Jaber, TK: AUTHOR

Abstract

The IEEE testability bus standard 1141.1 requires an asynchronous Test Clock (TCK) clock to allow the transfer of data/instruction over the bus. The TCK clock can be prone to glitches and noise which would result in erroneous data/instruction transfers. This disclosure describes a technique by means of which noise on the TCK clock line can be detected and reported so that data, and instruction transfer integrity can be preserved.

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Technique for Detecting Noise on the JTAG Bus Test Clock

      The IEEE testability bus standard 1141.1 requires an
asynchronous Test Clock (TCK) clock to allow the transfer of
data/instruction over the bus.  The TCK clock can be prone to
glitches and noise which would result in erroneous data/instruction
transfers.  This disclosure describes a technique by means of which
noise on the TCK clock line can be detected and reported so that
data, and instruction transfer integrity can be preserved.

      Also described is an FSM used on the 630 COP, which complies
with the IEEE testability bus standard 1141.1, for detection of noise
on the TCK line.

      The noise detection logic in question consists of a 4-bit FSM
and an additional bus signal called 'ATTENTION" used for reporting
noise or unexpected transitions on the TCK line.  The FSM is
illustrated in the attached figure.

      This FSM runs off of the main free running oscillator which
also clocks the rest of the 630 chip.  The TCK clock is completely
asynchronous and can transition at a frequency not to exceed 1/16 the
frequency of the main chip oscillator.  TCK can, of course, run at a
frequency that is slower than 1/16 the main oscillator frequency.
The noise detection FSM basically monitors the state of the TCK line
for as long as the TCK line should maintain a high state or a low
state and reports any unexpected transitions or glitches due to noise
via the 'ATTENTION' line.

      For examp...