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Twinaxial Poll Response Circuit for Card Manufacturing Test

IP.com Disclosure Number: IPCOM000112235D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 143K

Publishing Venue

IBM

Related People

Comp, C: AUTHOR [+3]

Abstract

Described is a circuit that responds to a twinaxial (IBM 5250 protocol) Poll command, and also provides attenuation that approximates 5000 feet of twinaxial cable. This circuit, along with some loadable Manufacturing Basic Assurance Test (MBAT) code thoroughly tests the twinaxial driver/receiver module(s) on Work Station Controller (WSC) cards.

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This is the abbreviated version, containing approximately 49% of the total text.

Twinaxial Poll Response Circuit for Card Manufacturing Test

      Described is a circuit that responds to a twinaxial (IBM 5250
protocol) Poll command, and also provides attenuation that
approximates 5000 feet of twinaxial cable.  This circuit, along with
some loadable Manufacturing Basic Assurance Test (MBAT) code
thoroughly tests the twinaxial driver/receiver module(s) on Work
Station Controller (WSC) cards.

      Fig. 1 is a diagram of the test setup that is used for testing
a twinaxial Work Station Controller (WSC) card with the Attention
Circuit and the Poll Response Circuit.  The Attention Circuit and the
Poll Response Circuit will be described in this disclosure.
Attenuation circuit - The Attenuation circuit (Fig. 2) consists of 10
resistors and 4 capacitors.  This attenuates the nominal twinaxial
output of 1.6 volts to about 150 millivolts.  This is similar to the
attenuation from a nominal 5000 foot twinaxial cable.  On either side
of this RC network would be a 55 ohm resistor from each signal to
ground.  This is the normal line termination value for twinaxial
cabling.  By using this network, the twinaxial driver (on the WSC) is
tested to assure it can drive 5000 feet of twinaxial cable; the
maximum supported cable length.  Also, the WSC card twinaxial
receiver is tested to assure it can receive a transmission from a
device (in this case, the Poll Response Circuit) 5000 feet away.
This type of verification has never been done before on twinaxial WSC
cards, at the manufacturing card tester.

      Poll Response circuit - The Poll Response circuit clocks in
data from the twinaxial cable every 500 ns.  When the Poll Response
circuit detects that data on the twinaxial cable has switched, it
synchronizes the clock to the transition.  This keeps the receiving
logic synchronized to the data.  If this is not done, then the slight
difference between the clock sending the data and the clock receiving
the data would quickly cause the data and receiving logic to get out
of sync, corrupting the data.

      The Poll Response circuit is designed to detect the data
sequence shown shown in Fig. 3.  The data is shown in 3 formats.  The
top line is the data as the 1's and 0's that the WSC microprocessor
works with.  The second line is the biphase encoded data.  A 1
becomes the sequence 1-0, 0 becomes the sequence 0-1.  The area
marked code violation is a violation of biphase encoding.  This along
with the two preceding biphase ones are used to denote the start of a
transmission (SOT pattern).  The third line is the waveform.

      The following discussion refers to Fig. 5 (i.e., State 0, State
1, etc) and Fig.  6 (i.e., block 1, block 2, etc).

      The Poll Response starts off in state 0, waiting for
transitions from the WSC.  The Poll Response Circuit receives data A
and B (Fig. 3) in sequence, as a single series of bits.  The data
passes through the twinaxial receiver (block 1) and is changed from a
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