Tektronix DC 5010 Anleitung Seite 252

Theory of Operation-DC 501 0
input from contending with the serial data output via U1114-
3. The microprocessor addresses U1313, causing a nega-
tive pulse on pin 14 (OLATCH) to latch the serial data in the
serial-to-parallel shift registers.
When the microprocessor is reading the serial data from
the Channel A and Channel B accumulators, pin 15 of
U1310B is set low at the same time pin 40 of U1410 is
configured as an input. The serial data are then read in as
five consecutive bytes. The microprocessor addresses
U1313 and uses pin 15
(m)
to latch data during the
serial read process.
Display lnterrupt Clock. The front panel keyboard and
displays are interrupt driven by the timing circuit consisting
of U1520A, U15208, and associated components. This cir-
cuit operates at approximately 1.1 kHz. The negative edges
of the signal on pin 37 of U1410 interrupt the micro-
processor, telling it to update the display and search for a
new keypush or control setting. The microprocessor ad-
dresses U1313 and uses pins 7, 9, 10, 11, and 12 during
this process.
Power Up Sequence. After the microprocessor and pe-
ripheral device U1410 have been reset at power up, the
DC 501 0 microprocessor generates the following sequence
of events.
Loads a 0 in the most significant bit position of the
front panel display.
Tests the RAM, starting at address $0000. If a RAM
failure is found, error code 340 will be displayed. The
RAM on the GPlB board is similarly tested, starting
at address $C0000.
Tests the four ROMs for byte location and deter-
mines the checksum. If a ROM error is found, error
code 361, 374, 375, 380, 381, 394, or 395 will be
displayed.
Checks to see if the Channel A TERM button is held
in, and, therefore, if signature analysis (SA) is being
requested. If the SA is not requested, the interrupt
registers in U1410 are enabled.
Initializes peripheral device U1410.
Performs a serial inputloutput test. If an error is
found, error code 313 will be displayed.
Sets up the hardware to determine the state of the
front panel, loads the serial-to-parallel shift registers,
and generates the relay strobe signals via pin 26 of
U1410.
Performs the counter chain (Channel A and Channel
B accumulators) integrity test. If this test fails, an
-
error code (320 through 324 and 329 for Channel A
or 330 through 334 and 339 for Channel B) will be
displayed.
Starts the measurement cycle by pulsing the master
reset line (pin 33 of U1410).
After the master reset pulse, the measurement gate
on pin 4 of U1200 (Diagram 3) is started. During the
measurement gate interval, the microprocessor is
continually reading the contents of the Channel A
accumulator for a count that is greater than or equal
to the number of averages requested by the user.
When that count is reached, the measurement gate
is unasserted and the microprocessor waits for the
signal on pin 35 of U1410 to go low, indicating the
end of the measurement cycle. The accumulators
are then read again for their final count and a new
measurement cycle is started after the result is cal-
culated and the display is updated.
Rear Interface Signals. The PRESCALE for U1410 (pin
29) operates as an input that indicates to the micro-
processor the presence of an external prescaling counter.
When an external prescaler is used, the microprocessor
multiplies the Channel A accumulated counts by 16 before . .
the display is updated.
The microprocessor interprets the reset input from
U1500A (Diagram 6) to pin 32 of U1410 as the electrical
equivalent of the front panel MEASUREMENT START/
STOP pushbutton.
NOTE
Complete data for all of the rear interface signals are
given in the Maintenance section of this manual.
PUSHBUTTONS AND
LEDs-DIAGRAM
@
The microprocessor uses five control lines and the 8-bit
data bus to communicate with the Pushbuttons and LEDs
and Display circuits. The five control lines are all derived
from U1313 located on Diagram 9.
The interrupt signal from the Display lnterrupt Clock
(Timer) circuit to U1410 (Diagram 9, previously discussed)
occurs approximately once every 900 ps. Each interrupt
-
causes the microprocessor to start a software routine for
servicing the Pushbuttons and LEDs, and Display circuitry.
REV OCT 1981