Inguard Microprocessor; Range And Function Control; Analog Filter - HP 3456A Operating And Service Manual

Digital voltmeter
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Mode1 3456A
!IN�LE �IRE
SHQMQARY
"
'5�
I
c
again clears U I 7 and disables NAND gate U14a. The
next negative-to-positive transition on the WRI line
(Ul3, pin 10) will begin another 9 count/shift cycle.
8-189. (nguard Microprocessor.
x 8 ROM (8-bit word, Read Only Memory) and a 64 x 8
RAM
(Random
memory» . The ROM is used for control of the Inguard
Circuits. The RAM is used for temporary storage of in­
struction data received from the Outguard and also for
measurement data that will will be sent to the Outguard.
An 8-bit bi-directional data bus is used for RAM data
transfer. The pP has no address lines but contains [WO
8-bit
quasi-directional
PT20-27) for input/output lines. These lines are used
for Inguard circuit cOnlrol during ranging, function
changes, measurements, etc.
8-190. The pP has an internal oscillator, clock circuits,
and an 8·bit time/counter. These are used for the tim­
ing, controlling, and measuring that takes place during
the Inguard measurement cycles. The iLP also generates
c
the ALE clock that is used by other A30 board circuits
and by the A/D Converter. The Input (from crystal
oscillator A3OQI) for Ul3's internal oscillator is 5.85
"
"
U19_
b
,
·sv,
Figure 8·40. Isolation LogiC, Transmitter.
The pP contains a I K
Access
Memory
(Read/Write
static ports (PTIO-17
""
S1<lfl
�HlSIU '
PAfIIILLfL •
c,.
10
!!ftJAL
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,
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c
'5V ,
Ul
: ·sv
!y�C
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• !IT
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COUNIf�
.-
MHz for 60 Hz and 4.875 for 50 Hz operation. The
ALE (Address Latch Enable) clock is 1/15 the frequen­
cy of A30Q I , or 390 kHz and 325 kHz respectively.

8-191. Range and Function Control.

8-192. General.
Schematic) and Schematic 6 (Range and Function Con­
trol Logic Schematic) for the following circuit descrip­
tion. Range and function set-up data is received via the
Isolation Logic from the OUlguard. This data is tern·
porarily stored by U I 3 and then passed to the Port Ex·
pander (U702) over
These 4 output lines are expanded to 16 lines by U702.
and
The Prog line (UI3, pin 25) is the Program strobe line
that is used to control the data transfer to U702. Ports
PTI5, PTI6. and PT25 (LGND, LMES, and HAF line
respectively) go directly to Inguard Switching circuits on
the A20 board.
8-193. LGND (Low Ground-Enable) and LMES (Low
Measure-Enable) are used to control FET switches in
the Input Switching circuits when Autozero is selected.
HAF (High Analog Filter-Enable) is used to control a
FET switch that enables the Analog Filter which is also
"IC��PMCn!Q�
"" ,
., .. ,
·sv
\
U19b
n-
Refer to Schematic 8 (lnguard Logic
110
lines PT20 through PT23.
Service
[1 .
."
.. ,
'"
.. 0
'"
, .... -....
8-35

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