Circuit Description
81
CG635 Synthesized Clock Generator
Q_OFFS:
Controls the high level offset of the front panel Q & -Q outputs. The output
offset, Q
OFFS
, is given by: Q
OFFS
§
1.834 × Q_OFFS – 2.150 V.
CMOS_AMPL:
Controls the amplitude of the front panel CMOS output. The output
amplitude, CMOS
AMPL
, is given by: CMOS
AMPL
§
1.648 ×CMOS_AMPL.
CMOS_OFFS:
Controls the low level offset of the front panel CMOS output. The
output offset, CMOS
OFFS
, is given by: CMOS
OFFS
§
0.519 × CMOS_OFFS – 1.063 V.
Microcontroller Output Latches
There are nine octal output latches to which the microcontroller writes data via the
Port-A bus to control the instrument. There are:
U501:
GPIB register address and control latch.
U502:
DDS register address and control latch.
U506:
Front panel seven-segment (odd digit) segment enable latch.
U507:
Front panel seven-segment (even digit) segment enable latch.
U508:
Front panel display and keypad strobe latch.
U509:
Front panel LED lamp enable latch.
U510:
RF reference and RF PLL bandwidth control latch and CMOS enable.
U511:
Programmable ECL divider load value.
U512:
Band select, output enable, PRBS enable, LVDS enable
Microcontroller Display and Keypad Scanning
Four of the octal latches (U506-U509) are used to refresh the front panel LED displays
and scan the keypad for key presses. The front panel display and key pad scanning is
controlled by seven strobe lines: STB0 to STB6. Each strobe line enables two
seven-segment displays, up to six LED lamps and the scanning of up to six keys. The
display refresh consists of eight periods of 1 ms duration; seven periods to refresh the
entire display and scan the keypad and an eight period to intensify/blink one of the
seven-segment display digits to show which digit would be affected by a
step-up/step-down key press. The sequence of that operation is outlined here.
1.
At the start of each 1 kHz real-time interrupt the microcontroller writes all zeros
to U508 to disable all of the displays.
2.
Data for the next strobe interval is loaded into the U506 (odd digit segments),
U507 (even digit segments), and U509 (LED lamps.) Writing a “0” will turn
“on” the corresponding segment or lamp, writing a “1” will turn it “off”.
3.
A single “1” is written to U508 to enable a single strobe line.
