HP 1660CP Series User Manual page 294

The Analyzer Hardware
Logic acquisition board theory
acquisition mode, it is available as a data channel. The clock/data channel is
also available as a data channel in timing acquisition mode. Eight
(HP 1660CP), six (HP 1661CP), four (HP 1662CP), or two (HP 1663CP)
clock/data channels are available as data channels; however, only six
clock/data channels can be assigned as clock channels in the HP 1660CP and
HP 1661CP. All clock data channels available in the HP 1662CP and
HP 1663CP can be assigned as clock channels.
The cables use nichrome wire woven in polyarmid yarn for reliability and
durability. The pods also include one ground path per channel in addition to a
pod ground. The channel grounds are configured such that their electrical
distance is the same as the electrical distance of the channel. The probe tip
assemblies and termination modules connected at the end of the probe cables
have a divide-by-10 RC network that reduces the amplitude of the data
signals as seen by the circuit board. This adds flexibility to the types of
signals the circuit board can read in addition to improving signal integrity.
The terminations on the circuit board are resistive terminations that reduce
transmission line effects on the cable. The terminations also improve signal
integrity to the comparators by matching the impedance of the probe cable
channels with the impedance of the signal paths of the circuit board. All 17
channels of each pod are terminated in the same way. The signals are
reduced by a factor of 10.
Comparators
Two proprietary 9-channel comparators per pod interpret the incoming data
and clock signals as either high or low depending on where the
user-programmable threshold is set. The threshold voltage of each pod is
individually programmed, and the voltage selected applies to the clock
channel as well as the data channels of each pod.
Each of the comparator ICs has a serial test input port used for testing
purposes. A test bit pattern is sent from the Test and Clock Synchronization
Circuit to the comparator. The comparators then propagate the test signal on
each of the nine channels of the comparator. Consequently, all data and clock
channel pipelines on the circuit board can be tested by the operating system
software from the comparator.
Acquisition
The acquisition circuit is made up of a single HP-proprietary ASIC. Each
ASIC is a 34-channel state/timing analyzer, and one such ASIC is included for
every two logic analyzer pods. All of the sequencing, pattern/range
recognition, and event counting functions are performed on board the IC.
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