1730–Series Theory of Operation
4–19
(X5, BLANK DOT, LINSEL, and 2H SWP PH). Pin 24 is the external
communications enable that controls the Auxiliary interface.
Pins 13, 14, and 15 input horizontal (line) sync and vertical (field) sync, to
decipher line select data and real-time switching functions (A/B and Low Pass/
Flat switching). The period for the FIELD, pin 12, determines the phase of the
60/50 control line. The status of this line is held permanently high (1730) or
permanently low (1731) for single standard instruments by the positioning of
J504. In the 1735 the jumper is not used and the Microprocessor determines the
level output on this line. 60 Hz (NTSC) mode of operation is selected for field
rates greater than 55 Hz, and 50 Hz (PAL) mode for field rates less than 55 Hz.
If signal field rate is close to 55 Hz, the standard selection may be indeterminate
and oscillate between 50 and 60 Hz. Automatic standard switching is delayed
from the signal switching by several video frames, to ensure that false switching
does not occur. If loss of reference occurs, the current standard is maintained
until reference is restored. The level of the 60/50 output dictates selection of the
Chroma filter and the line numbering for LINE SELECT.
Pins 10 and 11 are the Auxiliary bus (TXD pin 11 and RXD pin 10). U809B and
C are buffers for this bus structure which connects directly to a 1720-Series
through the rear-panel AUXILIARY connector.
Pin 17 (RD) is the remote input enable for U731, the REMOTE input buffer and
U809A, the REMOTE STORE buffer. Pin 16 (WR) enables readout DAC
(U325), clocks the I/O Data Latch (U532), and enables the internal registers in
the LED Driver (U407).
The functions of the control lines, originating on the Microcontroller diagram,
are shown in Table 4–1. The active condition of the line, and the expected result,
when active, are detailed here.
Table 4–1: Control Line Functions
Signal Line State Result
X5 High Enables 5X Vertical Magnifier. (U522)
BLANK DOT High Blanks between dots in Line Select readout. (U522)
LINSEL High Unblanks the CRT for Line Selected line. (U522)
2H SWP PHASE High Resets 2H Sweep Generator for Line Select and realĆtime
switching functions. (Q626)
RXD ĆĆĆĆ Used in serial port diagnostics and Auxiliary. (U809B)
TXD ĆĆĆĆ Sends data to companion 1720ĆSeries. (U809A)
CAL DR 100 kHz pulse to Calibrator. (U331B)
CAL Low Enables Calibrator. (U532)
ROEN High Enables readout in Line Select. (U532)
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