Chapter 8: Theory of Operation
Acquisition Theory
155
Interface and GPIB Board (A21)
The Interface Board (A21) has four 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.
• Acquisition control for segmented memory acquisition.
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.
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 Interface & GPIB board provides high-speed access to
oscilloscope configuration settings.
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