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Microprocessor Board Theory
The microprocessor board contains the system
memory, all the interfaces for the mainframe
peripherals, the intermodule bus monitor, and the
optional board module interface.
The mainframe peripheral interfaces are selected
by the microprocessor through the peripheral
demultiplexer and peripheral decoder.
Using the three most significant microprocessor
address bits, the peripheral decoder selects the
system ROM and RAM, the display RAM, and the
module interface.
The peripheral demultiplexers select the HIL
interface, the HP-IB and RS-232C interfaces, the
color palette, and the disk drive interface.
With the HP 16500A microprocessor board
containing ROM version 00.00, the system
memory consists of 64 Kbytes of ROM and
1 Mbyte of RAM. With the HP 16500A
microprocessor board containing ROM version
00.20, the system memory consists of 64 Kbytes
of ROM and 2.5 Mbytes of RAM. Stored in ROM
is part of the operating system, the power up
self-tests, the disk drive instructions and the
Human Interface Link (HIL) driver.
The Hewlett-Packard Human Interface Link
(HP-HIL) is the interface between the
microprocessor and the front-panel board. In the
write mode, the interface controller serializes the
8-bit data and transmits it 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.
The display RAM consists of eight 64 K by 4-bit
RAMs and one 4-bit shift register for each RAM.
Each RAM and shift register pair represents one
color plane in the display system. The output of
the color palette is an analog voltage of 0 V to
-1.0 V for each of the primary colors (Red, Blue,
Green) and is fed to the color module.
HP 16500A/16501A - Service
The HP 16500A 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 HP 16500A mainframe RS-232C interface is
compatible with standard RS-232C 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-232C communication lines.
The main components of the disk drive interface
are the drive controller and the digital data
separator. The controller provides the interface
between the microprocessor and the two disk
drives. It also performs all functions necessary to
write or read data to or from the disks. Data
between the microprocessor and disk drives are
serialized by the drive controller. The function of
the digital data separator is to synchronize data
between the interface and disk drives.
The module interface provides microprocessor
access to the acquisition and stimulus boards that
are plugged into the mainframe. The intermodule
bus monitor provides the means for time-aligning
module trace data on screen. This function is
performed by a 100-MHz acquisition device,
operating in the transitional timing mode.
6-5
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Troubleshooting
