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Chapter 5 Theory of Operation
Main Gate Array
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5
Main Gate Array
See “A1 Main Gate Array Schematic” on page 187.
U302 is a Field-Programmable Gate Array. When RESET* is asserted,
U301 serially loads the gate array with its contents. U302 asserts
MAR_AWAKE* to indicate to the CPU that it is loaded and ready.
The Main Gate Array performs many functions within the instrument
including:
• Main CPU address decoding and bus handshaking. It detects two
address ranges; one for internal register programming and one for
accessing devices on the shared bus (including DSP program RAM,
DSP data RAM, and the Synthesis IC control registers.
• DSP and Waveform RAM bus interface.
• Timers. U302 has two internal timers. One timer is used for internal
trigger operations. The other timer generates the front panel LCD clock.
• DSP serial communications. This serial communication allows the
Main Gate Array to send incremental, low impact changes in the
waveform to the synthesizer without affecting the continuity of the
waveform or modulation output.
• QSPI scanned serial bus support. The QSPI data is decoded into
signals that control the analog output path attenuators and relays.
Additionally, the QSPI data can be set to a “loop-back” mode to test
the external data path and shift registers.
• Provides the serial interface required to load the configuration of the
Synthesis Gate Array, U1201.
• System DAC control. The Main Gate Array controls and times the
System DAC operations, including the sequence; disconnect the
System DAC from the present sample-and-hold output, latch new
data into the DAC, change the multiplexer address to the new output,
allow the System DAC to settle, and then connect the System DAC to
the new sample-and-hold circuit.
U303 and U304 act as a 16-bit serial-in parallel-out shift register.
The register converts serial data from the QSPI output of the Main CPU
to a parallel word. Registers U305, U306, U307, and U308 capture the
converted words and drive various logic-level signals. Registers U305
and U306 are devoted to driving relays.
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