>Audio goes to a speaker and a phone jack and was never mixed with the video in >a composite output. > Some third party may have made an NTSC, National Television Standards > Committee, conversion > to allow for a second monitor but I never saw it. Apple's earlier Apple II > line did put out NTSC video > and you could run a TV monitor from that but even there I don't think the > audio was ever mixed with the video.
That would have been a good trick on a ][. :) There wasn't an audio signal to encode. Apple ][ sound came from adressng a 16 byte block of memory, which toggles the speaker. Not by writing.a value; it w done straight from the address lines, which wren't decoded past the last four bits for this and some other purposes (the cassette, and I think th game inputs and outputs). When those twelve high bits appeared on the address line, the flip-flop was toggles. Toggle fast enough, and you got a tone. As for video, the base composite video is the greyscale image and horizontal and vertical sync. Color is done by drift from the 3.58 MHz "color burst" subcarrier attached to this signal--which is why color home computers on televisions never went past the density of the ][. The ][ finagled color by tickling that carrier; the pixels were appearing at twice that frequency on the screen, and it shifted them a half pixel to get color in hires mode (and this also causes the purplish tint of text on most monitors until the Rev 7 or so motherboard). -- The Hawkins Law Firm Richard E. Hawkins, Esq. (702) 508-8462 [email protected] 3025 S. Maryland Parkway Las Vegas, NV 89109 -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
