Commodore VIC-20 User Manual page 18

4
The VIC 20 User Guide
configuration. Instructions for connecting the printer and disk drive to the
VIC 20 are provided later in this chapter.
Video Port
The VIC 20 produces the sound and pictures displayed on your
television by combining them into a signal called composite video. This
signal is sent out through the video port.
A video monitor (a television without a tuner) is able to convert the
composite video directly into pictures and sound. A television, however,
must be tuned to a particular channel. That signal is produced and
combined with the composite video by the RF (radio frequency) modulator
(the small black box in Figure 1-1).
When you use the VIC 20 you can select either channel 3 or channel 4
by flipping the channel switch on the side of the modulator.
Expansion Interface
The expansion interface gives you access to the computer's memory
lines. Through it you may increase the memory size of your VIC 20 to as
much as 32K (more than 32,000 bytes).
NOTE: Increasing the memory size may cause the computer's memory
to be reconfigured. This will cause the screen display information and some
parts of user memory to be moved to other locations in memory. Generally,
this will cause no noticeable changes. In some cases, however, it will cause
program run failures. Look at the memory map in Appendix B for specific
information on memory expansion and reconfiguration.
Video Display
When you first power up the VIC 20 it displays 23 rows with 22
characters per row. The computer generates these characters by lighting the
appropriate pattern of dots within an 8 X 8 matrix. This is illustrated in
Figure 1-3. The VIC 20's character set is quite extensive, containing 256
letters, numbers, and symbols.
It
is also possible to program custom
characters for special applications. This will be discussed in Chapter 6.