Agilent Technologies 46A, 45A, 54835A manual Acquisition Modes, Scope Interface Board

Chapter 8: Theory of Operation

Acquisition Theory

Analog Interface The Analog Interface provides analog control of functions in the acquisition circuitry. It is primarily DACs with accurate references and filtered outputs. The analog interface controls:

•Channel offsets

•Trigger levels

•Two logic trigger functions

Acquisition Modes

The Agilent Technologies 54835A provides two acquisition modes:

•2 GSa/s on each of the four channel inputs

•4 GSa/s on channel 1 and channel 3 inputs

The Agilent Technologies 54845A provides two acquisition modes:

•4 GSa/s on each of the four channel inputs

•8 GSa/s on channel 1 and channel 3 inputs

4 GSa/s In this mode, the scope uses all four channel inputs. Each channel can sample up to 4 GSa/s (for Agilent Technologies 54845A).

8 GSa/s In this mode, the scope only uses the channel 1 and channel 3 inputs. The ADC hybrids for the channel 1 inputs are routed to both the channel 1 and channel 2 ADC hybrids. The hybrids are time-aligned to sample 90° out-of-phase to yield a sample rate of 8 GSa/s. Channel 3 and channel 4 are combined in the same way (for Agilent Technologies 54845A).

Scope Interface Board

The Scope Interface Board has three primary functions:

•Interface the acquisition board to the motherboard system controller.

•Manage the waveform display, through an interface to the SVGA display board.

•Implement miscellaneous oscilloscope functions, including an RS-232 interface to the front- panel keyboard, a 32-bit timer, and non-volatile RAM.

Acquisition Board Interface The interface to the acquisition board consists of 16 data lines, 10 address lines, a R/W line, and read and write strobes. A second read strobe is used for reading acquisition data; the address latches are not used when this strobe is active.

Three lines are used to indicate run, trigger, and interpolator status; two control lines are used for trigger control and clocking.

There are two address ranges on the acquisition board; the first is used for reading acquisition data, while the second is used to access status and control elements of the board.

Waveform Display Management A PC video connector connects the scope interface board to the SVGA display board. The scope interface board accepts video clock and synchronization signals from the SVGA display board, and drives 16 bits of RGB data in 5,6,5 format to the display controller on the SVGA display board. The display driver will only substitute the PC video RGB data from the scope interface card for the other video data when the screen data matches the value specified in the display driver. In this way, the scope interface card can supply the waveform data from the acquisition system and have it properly multiplexed with regular video data for output on the flat-panel display.

Miscellaneous System Functions An RS-232 interface is used to communicate with the front panel keyboard. The connector routes transmit and receive, power supply bias and inhibit signals, and keyboard power to the keyboard. The interface functionality is contained in the FPGA. The data rate is 19.2 KBaud, with 1 start bit, 8 data bits (LSB first), and one stop bit, no parity. The keyboard itself has a controller that transmits and receives data through this interface.

Non-Volatile RAM (NVRAM) on the scope interface board provides high-speed access to instrument configuration settings.

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