Editing TRS-80 (section)

=== Video and audio===
[[File:TRS-80-graphics.svg|thumb|Layout of characters and pixels on the TRS-80 display<ref name=80Micro-June80/>]]
The color of the {{cvt|12|in}} KCS 172 RCA monitor's{{r|white198708}} text is faintly blue (the standard P4 [[phosphor]] used in black-and-white televisions). Green and amber filters, or replacement tubes to reduce [[eye fatigue]] were popular aftermarket items. Later models came with a green-on-black display.

Complaints about the video display quality were common. As Green wrote, "hells bells, [the monitor] ''is'' a cheap black and white television set with a bit of conversion for computer use".{{r|green198001}} (The computer could be purchased without the Radio Shack monitor.)<ref name="fylstra197804">{{cite magazine |url=https://archive.org/stream/byte-magazine-1978-04/1978_04_BYTE_03-04_Optimization#page/n49/mode/2up |title=The Radio Shack TRS-80: An Owner's Report |magazine=[[Byte (magazine)|Byte]] |volume=3 |issue=4 |date=April 1978 |access-date=October 17, 2013 |author=Fylstra, Dan |author-link=Dan Fylstra |pages=49}}</ref> CPU access to the screen memory causes visible [[flicker (screen)|flicker]]. The bus arbitration logic blocks video display refresh (video-RAM reads) during [[central processing unit|CPU]] writes to the VRAM, causing a short black line. This has little effect on normal BASIC programs, but fast programs made with [[assembly language]] can be affected. Software authors worked to minimize the effect, and many arcade-style [[List of TRS-80 games|games]] are available for the Tandy TRS-80.

Because of bandwidth problems in the interface card that replaced the TV's tuner, the display loses horizontal sync if large areas of white are displayed. A simple half-hour hardware fix corrects the problem.

The graphics are displayed at a resolution of 64×16 character positions on a screen measuring {{convert|7.5|in|cm}} wide and {{convert|6.625|in|cm}} tall.{{Sfn|Mazur|1983|p=386}} Each character is composed of a 2×3 matrix of pixels, and corresponds to one byte of the 1&nbsp;KB video memory used by the TRS-80. In each of those bytes, the first six bits control which pixel is displayed. The seventh bit is ignored, and the eighth toggles graphics mode.<ref name=80Micro-June80>{{cite magazine|url=https://archive.org/details/80_Microcomputing_Issue_06_1980-06_1001001_US|title=The Assembly Line|last=Barden|first=William |author-link=William Barden Jr.|magazine=[[80 Micro]]|date=June 1980|access-date=October 14, 2021|pages=22, 24}}</ref>{{Sfn|Mazur|1983|p=294, 297}} The reason that the seventh bit is ignored is due to the company's decision to have only seven 2102 static-RAM chips installed on the computer's motherboard instead of eight to keep the manufacturing cost low.{{Sfn|Technical Reference Handbook|1982|pp=34, 96–97}} Thus, there are no lowercase letters in the [[TRS-80 character set]] of an unmodified Model&nbsp;I, and the number of both graphics symbols and alphanumeric symbols is 64.{{Sfn|Mazur|1983|pp=258–259}} This can be worked around by deleting the unused bit and piggybacking an eighth 2102 chip onto another.{{Sfn|Mazur|1983|pp=28, 313–314}} The alphanumeric symbols are displayed in 5×7 matrices of [[pixel]]s.<ref name=80Micro-June80/> The 1978 manual for the popular word processor [[Electric Pencil]] came with instructions for modifying the computer. Although the modification needs to be disabled for Level&nbsp;II BASIC, its design became the industry standard and was widely sold in kit form,<ref name="reedlc">{{cite web |url=http://www.trs-80.org/electric-pencil-lowercase-modification/ |title=The Electric Pencil Lower Case Modification |access-date=27 February 2016 |author=Reed, Matthew}}</ref> along with an eighth 2102 chip. Later models came with the hardware for the lowercase character set to be displayed with descenders.

With higher-density RAM chips and purpose-built monitors, higher-resolution crisp displays are obtainable; 80×24-character displays are available in the Model&nbsp;II, Model&nbsp;4, and later systems.

The Model I has no built-in speaker. Square-wave tones can be produced by outputting data to the cassette port and plugging an amplifier into the cassette "Mic" line. Most games use this ability for sound effects. An adapter was available to use [[Atari joystick port|Atari joysticks]].{{r|williams198109}}