Start-Up; Timing And Clock Functions; Character And Command Sources - Zenith Z-29 User Manual

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5.2
THEORY OF OPERATION
START-UP
The CPU (Central Processor Unit) contains a portion of mem-
ory (ROM-Read Only Memory) which instructs the Terminal to
perform a series of tests to verify proper operation. At the suc-
cessful completion of these tests, all circuitry is reset (including
a built-in time clock). The system is then initialized by the pro-
9ramming in the program and expansion ROM(s) (permanent
program memory) and by the nonvolatile memories (you pro-
gram these while the Terminal is in the Setup Mode). Communi-
cation is established with a host computer (if present) through
the port you select during the Setup operation (normal or auxil-
ary).
TIMING AND CLOCK FUNCTIONS
In addition to maintaining a time clock function, the system also
uses various timing signals (clocking frequencies) to maintain
synchronization within the Terminal and to establish the com-
munication channel's baud rates (the rate at which information
is transmitted from a computer).
CHARACTER AND COMMAND SOURCES
Characters and Terminal commands (single or multiple byte)
may be received at the Terminal from any of three sources: the
keyboard, a host computer, or its own internal memory.
• When the Terminal receives character and terminal com-
mands are received from the keyboard, the Terminal CPU
processes them in accordance with the programming you
established when you set up the Terminal, or the instruc-
tions contained in its program ROM(s).
• Codes received from a host computer are passed through
the Terminal CPU, which strips the data from the transmit-
ted signal. The resulting code can be acted upon if it is a
command, or stored in your Terminal's memory if it is a
character.