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CHAPTER I I •
COMMAND INFORMATION
1.
GENERAL
This chapter provides the . . user with the information necessary
to develop application programs for use with the videodisc
player.
It contains a brief description of the programmable
memory and registers, describes the essential characteristics
of a user program, and presents a comprehensive discussion
of commands for use in programs and for external control of
the player.
Throughout the remainder of this manual, extensive reference
is made to hexadecimal values.
Hex values are denoted by
single quotes ('F21) or by a leading asterisk (*F2).
Although
not standard notation, this method has been adopted because
the video display employs the asterisk convention to display
many of the commands that are entered into RAM during Programming
Mode.
2.
RANDOM ACCESS MEMORY
The videodisc player includes a
Z80 microcomputer, an EPROM
that contains the basic operating system of "the player, and
eight kilobytes of Random Access Memory (RAMh of whiCh lK
(1024 bytes) is available to the user.
The RAM performs a
dual function, serving"" as both addressable program command
memory and user registers.
This coexistence requires the
RAM to be used both for program storage and as a group of
512 registers that the program can reference.
Because memory
and registe'rs may overlay each
other'~"
the programmer must'
understand how each is structured and addres'sed.
'
A.
Addressable Memory
Each RAM memory location is one eight-bit byte.
Memory
locations begin at address 0 and continue to address 1023.
Locations 1022 and 1023 are not normally used' for program
storage, but are
reserve~
for use as Register O.
Program data, i.e., arguments and commands, are stored
in coded format.
Each argument digit and each command
require one byte, and thus occupy one memory location.
For example, the value 1536 stored within a program as
a command argument occupies four bytes and has the hexadecimal
format *OF*AF*4F*6F.
TP109 Version 2.0
- 8 -
April 1984
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