The graphics capabilities of the VIC chip (6560/6561) are limited but flexible. At startup the screen shows 176×184 pixels, with a fixed-color border to the edges of the screen. Since a PAL or NTSC screen has a 4:3 width-to-height ratio, each VIC pixel is much wider than it is high. The screen normally shows 22 columns and 23 rows of 8-by-8-pixel characters; it is possible to increase these dimensions up to 27 columns, but the characters would soon run out the sides of the monitor at about 25 columns. Just as on the PET, two different 256 character sets are included, the uppercase/graphics character set and the upper/lowercase set, and reverse video versions of both. Normally, the VIC-20 operates in high-resolution mode whereby each character is 8×8 pixels in size and uses one color. A lower-resolution multicolor mode can also be used with 4×8 characters and three colors each, but it is not used as often due to its extreme blockiness. The VIC chip does not support a true bitmap mode, but programmers can define their own custom character sets. It is possible to get a fully addressable screen, although slightly smaller than normal, by filling the screen with a sequence of different double-height characters, then turning on the pixels selectively inside the RAM-based character definitions. The Super Expander cartridge adds BASIC commands supporting such a graphics mode using a resolution of 160×160 pixels. It is also possible to fill a larger area of the screen with addressable graphics using a more dynamic allocation scheme, if the contents are sparse or repetitive enough. This is used by the port of "Omega Race". The VIC chip has readable scan-line counters but cannot generate interrupts based on the scan position. The two VIA timer chips can serve this purpose through an elaborate programming technique, allowing graphics to mixed with text above or below it, two different background and border colors, or more than 200 characters for the pseudo-high-resolution mode. The VIC chip can process a light pen signal (a light pen input is provided on the DE-9 joystick connector) but few appeared on the market. The VIC chip outputs composite video. Commodore did not include an RF modulator inside the computer's case because of FCC regulations. It can either be attached to a dedicated monitor or a TV set using the external modulator included with the computer. The VIC chip has three pulse wave generators and a white noise generator with an overall volume control and mono output.