HP 200 Series Hardware Support Document page 28

20
Functional Description
The boot ROM contains 48K bytes of software instructions. These are the first instructions executed
by the CPU at start-up, and serve to initialize the 9817, run the turn-on 'self-test and load the
language system.
The keyboard and speaker interface consists of an 8042A keyboard controller IC, an HP-HIL
(Hewlett-Packard Human Interface Loop) controller, a 76494 tone generator and a speaker driver.
The keyboard controller provides a system interface to the HP-HIL controller and to the tone
generator, as well as system timer functions. The tone generator consists of three programmable
tone generators and a programmable noise source. It produces an analog audio signal to the
speaker driver. The speaker driver is an audio amplifier and produces a signal capable of driving the
speaker mounted on the chassis. The HP-HIL controller provides an interface between the
keyboard controller and the loop, and handles all HP-HIL external protocol. The loop is a four-
wire, serial daisy chain, consisting of input devices such as a keyboard, joystick or mouse.
The built-in HP-IB interface contains all the circuitry required to communicate via an HP-IB cable.
Direct Memory Access (DMA) support electronics is included, so that DMA via HP-IB is possible if a
DMA card is installed in an accessory slot.
The built-in RS-232 interface contains all the circuitry required to communicate via an RS-232
cable. It operates on a dedicated 2.4576 MHz clock.
The input/output section contains switch blocks for selecting RS-232 baud rate, remote terminal,
handshake, parity options, parity enable, number of stop bits, character length and control line
defeat.
The chip select decodes buffered address lines BA16 thru BA23 into chip select signals for the
internal HP-IB interface, the internal RS-232 interface and the keyboard.
The processor board contains switches for selecting HP-IB system controller, short or long memory
test and continuous self-test.