3.3 Assembly Circuit Descriptions
The following sections describe the circuit theory and operation of specific assemblies in the
GT 9000 Microwave Synthesizer. Each section heading includes the PC assembly number as
shown in the related circuit drawings.
3.3.1
Front Panel Interface — PC Assembly A1
The Front Panel Interface PC assembly interfaces the front panel and the computer. This
includes front panel data entry (in the form of keystrokes or knob movement) as well as front
panel data display.
U1, a 4-to-16 decoder, decodes the chip selects for the different front panel displays and
interfaces. U14A thru U14D provide the individual chip selects for the front panel ENTRY
MENU displays, which are gated by the UR/UN line. U2A provides a load signal for loading
data to these displays.
The U3 Keyboard decoder, where D1 thru D11 represent columns and S1 thru S8 are rows,
identifies keys pressed and outputs information to the computer bus via the U5 buffer. U15B
provides a clock circuit for scanning the keyboard. Whenever the keyboard is active, U15A
detects the Data Available line and causes an interrupt to be generated by U6A and U11B. When
the computer responds with a chip select from U1 indicating that the keyboard can be read, the
interrupt is cleared via U6A. U7A and U11A activate the Memory Ready line which slows the
CPU as required for read cycles to occur.
When the front panel knob is turned, the optical decoder generates pulses at U8A and U8B; the
flip-flops of U8 are set so that the output at U8-9 indicates which way the knob was turned.
U8-5 flips, generating an interrupt via U11C. When the computer selects the knob to be read, a
chip select is received at U7B from U1 to clear the interrupt.
U4, U5, U9, and U18 provide buffers for computer bus interface.
U12 is the Configuration ROM. It stores the information such as the frequency range and what
options are installed. It is also programmed to hold various characterization data.
U13 is a non-volatile RAM chip to store the current unit settings when the power is turned off.
It also stores multiple unit setups in memory locations 0 thru 9.
3.3.2
IEEE / TIMER — PC Assembly A2
U10 is the interrupt timer for the CPU. It is clocked by the oscillator consisting of Y1, C10, and
C12.
U8 and U9 provide for the addition of an RS-232 interface feature which is not yet implemented.
U12, U13, and U14 operate the remote control interface, which conforms to the IEEE-488
standard.
U3 decodes chip selects for the circuits on this board. U11 acts as a buffer for certain computer
bus lines.
The outputs of flip-flop U5 latch attenuator data; U7 and U4 provide the proper logic levels for
driving the attenuator. The outputs of flip-flop U6 latch miscellaneous computer control lines.
Model GT 9000 Microwave Synthesizer
3-18
Manual No. 120AM00250, Rev C, September 1998
Summary of Contents for GT 9000
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