Radio Shack Quick Printer II Reference Handbook

System Block Diagram
The 80 integrated circuits contained in the TRS-
80 can be broken down into about 10 major
sections. Figure 1 shows these sections as they
relate to other sections. The heart of the system
is definitely
the CPU (Central Processing Unit).
You might
consider the CPU as being a very
dumb calculator circuit. It may be dumb, but
it's a fast dummy. Most of the leads on the CPU
Cire data linesand address lines. The CPU tells the
address bus where the data it wants is located,
and the data bus is a good place for the informa-
tion to come back to the CPU. The address lines
are
outputs from the CPU. They never receive
data or addresses from other sections. The data
lines on the other hand can give or receive data.
AC
ADAPTER -=:::;
POWER
SUPPLY
5,
~
E
L.
DATA
READ
I----t>
DATA OUT
CONTROL
CPU
WRITE
GROUP
ROM
CS
IN
OUT
ADDRESS
ADDRESS
d
If the CPU has to be the heart of the system, the
ROM (Read Only Memory) could be considered
the brains. The ROM tells the CPU what to do,
how to do it and where to put it after it's done.
Without the ROM, the CPU would just sit there
and oscillate. When power is first applied to the
system, the CPU has just enough smarts to out-
put an address to the ROM that locates the
CPU's first instruction. The ROM shoots back
the first instruction and then the two really start
communicating. In less than a second, the CPU,
under ROM supervision, performs all the house-
keeping necessary
to get the system alive and a
"READY" flashes on the screen.
ROM
If the CPU misses that first piece of ROM data,
then it may go bananas. It may tell the ROM
that it is ready to load a tape so the ROM tells it
how to do that. The Tape Recorder turns on.
But since the CPU is now playing games in the
video memory, who cares about the tape? The
CPU operates at about 2 MHz; therefore, digital
screw-ups seem
instantaneous.
~
~
Remember that the CPU is the work horse and
the ROM is the boss. The ROM tells the CPU
how to do it, when to do it, and where it put it.
9

Radio Shack Quick Printer II Specifications

General

Brand	Radio Shack
Model	Quick Printer II
Category	Desktop
Language	English