Tektronix 1730 Series, Instruction Manual

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1730–Series Theory of Operation
4–21
U726 is the power down detection circuit. It detects the loss of instrument
power in time for the NOVRAM (U725) to execute a save operation. When the
+5 V supply drops a few hundred millivolts, pin 7 is pulled low, which pulls the
STR for U725 down, causing it to Store its current status. The front-panel and
Auxiliary (Store/Recall) data is saved in a matter of milliseconds when the
power starts to drop below safe operating levels. U727 is a three-terminal
regulator operating from the +15 V supply, which comes onto the circuit board
from the main Power Supply. As soon as the +15 V raises enough to provide a
+5 V output from U727, U725 recalls the data saved so that it will be available
to the Microprocessor when all supplies are up to their operating tolerances.
U884 is a serial-in/parallel-out register that is loaded with the real-time switching
data from the Microprocessor serial port (pin 10) whenever pin 24 of U522, goes
high. When pin 24 is high, the serial input of U884 is enabled and the external
communications input, through U809B, is disabled. The eight bits of serial data
now in the internal register are clocked out, in parallel, by the leading edge of H
(line) Sync, which is the clock signal driving U884 pin 12.
U527 is the Address DE-MUltipleXer (Demux) used to decode the lower eight
bits of the address line. Even though both addresses and data share the same
Microprocessor port, only addresses are present when U527 is clocked by the
Microprocessor ALE output.
U325, through U231A and B, drives the X and Y axes of the dot-scanned line
select CRT readout. U325 is a dual D/A Converter (DAC) whose internal
registers are loaded from the Data/Address bus and clocked by the Microproces-
sor WR output.
U532 is the data latch outputting control signals to the 1730-Series non real-time
switching and the readout enable (ROEN). The addresses are loaded from the
Address Demux (U527) and clocked out by the Microprocessor WR output. The
ROEN operates in conjunction with the Microprocessor Blank Dot output
(pin 26) in order to display the data output from U325 on the CRT.
U331 divides down the Microprocessor ALE output to generate Cal Drive.
U331 is enabled by the CAL from the I/O Data Latch, U532.
The front-panel LEDs are driven in six common banks by U407. U305 provides
a common current drain that is enabled by U407. Data registers in U407 are
written into by the Microprocessor over the eight-bit address bus and read out to
front-panel LEDs when WR goes low.
Switch Control
Address Demux
Readout Drive
I/O Data Latch
Cal Drive
LED Drive