PS2 Interface
The PS2 Interface connects the external keyboard and mouse to the 16500C backplane. The
interface is made up of a single PS2 controller and buffers. The PS2 ports are on the I/O board,
and are connected to the CPU board through a cable.
HIL Interface
The Hewlett-Packard Human Interface Link (HP-HIL) is the interface between the
microprocessor and the HP 16500C touch screen. In the write mode, the interface controller
serializes the 8-bit data and transmits the data to the devices on the link. In the read mode,
the data is fed to the interface controller in serial format and to the microprocessor in parallel
format.
HP-IB, RS-232-C, and Centronics Interface
The HP 16500C interfaces to HP-IB as defined by IEEE Standard 488.2. The interface
consists of two octal transceivers and an HP-IB controller. The controller relieves the
microprocessor of the task of maintaining HP-IB protocol. The two transceivers provide data
and control signal transfer between the bus and the controller.
The RS-232-C interface is compatible with standard RS-232-C protocol. The interface consists
of a controller, an input buffer and an output buffer. The controller serializes parallel data
from the microprocessor for transmission. In the receive mode, the controller converts
incoming serial data to parallel data for the microprocessor. The controller also generates all
the different baud rates and formats available with the mainframe. The input and output
buffers transfer data and control signals to and from the RS-232-C communication lines.
The Centronics parallel printer interface is made up of a multiplexer, buffers and termination
resistors. The buffers connect the microprocessor data bus directly to the parallel printer port
through the termination resistors. The multiplexer is used to control the data flow direction
and write control. The parallel printer port and RS-232-C port are on the I/O Board, and are
connected to the CPU board through a cable. The HP-IB port is connected directly to the CPU
board through a cable.
Display RAM, Color Palette, and CRT Control
The HP 16500C CRT display is driven by a Color Palette and CRT Control supported by
256 KBytes of video RAM. A single RAMDAC functions as the Color Palette for the
eight-plane color monitor. RGB signals are provided by the RAMDAC. The RAMDAC sends
an analog signal of 0.0 to -1.0 Volts for each of the primary colors (Red, Blue, Green) to the
color module. Horizontal and vertical sync signals are provided by a CRT controller.
Hard Disk Drive Interface
The Hard Disk Drive Interface is made up of two octal transceivers and three buffers. The
octal transceivers link the hard disk drive’s 16-bit data I/O port with the microprocessor data
bus. The buffers link the hard disk drive’s control signals with both the address bus of the
microprocessor and the peripheral interface signals so that the hard disk drive resides at a
virtual address in read and write modes. The hard disk drive controller resides on the hard
disk drive.
Flexible Disk Drive Interface
The main components of the Flexible Disk Drive Interface are the disk drive controller and
buffers. The disk drive controller provides the interface between the microprocessor and the
flexible disk drive. The controller also performs all functions necessary to write or read data
to or from the disks. Data directed to the disk drive from the microprocessor is serialized by
the disk drive controller.
Theory of Operation
The Microprocessor Board
8–8
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