Agilent Technologies 54830 Series, Service Manual

Page: 166 / 170

Chapter 8: Theory of Operation
Acquisition Theory
8–9
Interface and GPIB Board (A21)
The Interface Board (A21) has three primary functions:
• Interface the acquisition board to the motherboard system controller.
• Implement miscellaneous oscilloscope functions, including an RS-232 interface to the front-
panel keyboard, a 32-bit timer, and non-volatile RAM.
• GPIB remote control interface.
The GPIB Interface provides IEEE-488.2 standard bus services for the oscilloscope. The card
interfaces the bus to the motherboard system controller, allowing the system controller to receive
and process GPIB commands and return data to the bus. The circuit consists of three main
components. The GPIB controller provides an interface between the microprocessor system and
the GPIB in accordance with IEEE 488 standards. An 8-bit data buffer and 8-bit control line
buffer connect the GPIB controller to the GPIB bus. The GPIB is a 24-conductor shielded cable
carrying 8 data lines, 8 control lines, 7 system grounds, and 1 chassis ground.
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 oscilloscope
interface board to the display board. The oscilloscope interface board accepts video clock
and synchronization signals from the display board, and drives 16 bits of RGB data in 5,6,5
format to the display controller on the display board. The display driver will only substitute
the PC video RGB data from the oscilloscope interface card for the other video data when
the screen data matches the value specified in the display driver. In this way, the oscilloscope
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 oscilloscope graphics board provides high-speed access to
oscilloscope configuration settings.