HP 5334B - Executive Block Circuit Description

8-160. The Executive MCU has four &bit UO ports, for a total of 32 VO hes. Eight lines are used to communi-
cate over the Executive Data Bus. Another
8 lines are used for communications via the Measurement Data Bus.
The remaining 16 lines are used for addressing, controlling, and monitoring functions.
8-161. The &bit Executive Data Bus connects the Executive MCU to the HP-IB MCU (U17), and the front
panel display drivers
(U1 and U2) on the A2 board. The second &bit bus, the Measurement Data Bus, connects
the Executive MCU to the Measurement MCU
(U29) which controls the Measurement Block and the input sig-
nal conditioning.
8-1 62. Executive Block Circuit Description
8-163. The Executive MCU (U19) continuously strobes the keyboard through the demultiplexer (U32) with the
ABCD address lines. At the same time, it scans the keyboard directly over the YO to Y3 lines. The Executive
MCU sends a
Cbit binary code sequence over the ABCD lines to the demultiplexer. The binary sequence con-
tinuously cycles through 9 of 16 possible combinations. The MCU
(U19) is programmed to skip over the un-
needed codes.
8-164. The 4-to-16-be demultiplexer decodes each Cbit code in the binary sequence. The two ENABLE in-
puts of the demultiplexer are maintained in the logical
"0" state so data is continuously accepted. The informa-
tion is then transmitted to the selected output as determined by the
Cline (ABCD) input address. As the ABCD
lines cycle through the sequence, each output line (XO to X8) goes
LOW in turn.
8-165. The first nine output limes of the demultiplexer (OX to X8) go to the front panel keyboard, where they
form a 9-by-4 matrix with the YO to Y3 lines. When a key is pressed, one of the strobe lines (XO to X8) is
shorted to one of the scan lines (YO to
Y3). The MCU (U19) determines the key that was pressed by detecting
which strobe line and which scan line went
LOW simultaneously.
8-166. The two additional output lines from the demultiplexer
(XI2 and X14) control the Measurement MCU
(U29). Line X12 is connected to the INTERRUPT REQUEST line and XI4 is connected to the RESET line.
When activated externally, the Executive
MCU uses X14 to reset the Measurement MCU and begin program ex-
ecution,
e.g., when the RESET key is pressed, or when power is applied to the instrument. The interrupt request
line
(X12) is used to initiate a data transfer from the Executive MCU to the Measurement MCU.
8-167. After the Executive MCU interprets and decodes instructions from the front panel keyboard or the
HP-
IB MCU, it sends the appropriate instruction code to the Measurement MCU. In turn, the Measurement MCU
programs the Measurement Block, configures the Input Amplifiers as instructed, and makes a measurement.
8-168. When a measurement is complete, the Measurement MCU sends the result over the Measurement Data
Bus to the Executive MCU. The measurement data is interpreted and formatted by the Executive MCU, then
sent over the Executive Data Bus to the front panel display and the HP-IB MCU.
8-169. The 4-MHz clock oscillator
(U18) provides the clock signal for all three MCUs in the HP 5334B. The 4-
MHz output frequency is determined by quartz crystal Y2. The clock signal goes to the XTAL2 line (pin 2) of
each microcomputer.
HP 5334B - Service Manual
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