Radio Shack TRS-80, Service Manual, Page: 4 / 44

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SYSTEM DESCRIPTION
The MC-10 Micro Color Computer is a fully
expandable microprocessor system. It is com-
posed of a 6803 central processing unit, 4K of
static RAM, 8K of Basic ROM, and a 6847 video
display generator. The microcomputer is also
interfaced to a 48-key keyboard and provides
the logic to execute a 1500 Baud cassette inter-
face and a RS-232 serial interface. The system
operates on a common color burst frequency
of 3.579545 MHz. This main clock is divided by
4 in the CPU to yield an operating speed of 0.89
MHz.
In operation, the 4K of static RAM is shared
between the CPU and the video display gene-
rator. This time multiplexing is based on the
processor clock E. The CPU will be granted
access to the RAM (upon request) only during
the high state of E. This allows efficient usage
of the RAM with no waiting by the CPU and no
visible conflict on the display.
The 6847 VDG provides a display on a TV
screen of 32 characters by 16 rows. It also
allows a 64 x 32 semigraphics mode with eight
colors. This display utilizes a minimum amount
of system RAM (512 bytes).
The final elements of the microcomputer sys-
tem are the I/O devices. The MC-10 is interfaced
to a 48-key keyboard which generates the
codes for upper and lower case characters,
graphics symbols, and single stroke keyboard
entry. The computer also provides a 1500 baud
cassette interface for fast and reliable data and
program storage and a limited signal RS-232C
interface. The RS-232C interface allows either a
printer or a modem to be used with the MC-10.