Daphne
Daphne is the original version of Denise and is also known as 4702. It was designed by Dave Dean, Jay Miner, Ron Nicholson and Mark Shieu. Its resolutions were originally 640 x 400 for an RGB monitor or 320 x 200, optimized for a composite monitor or television set, which a lot of home computer users still had for a display. Early in Lorraine’s development, Jay was uncertain whether or not it would have RGB video in the final product. By late 1983, Ron had devised a feature initially known as “hold and control” mode, later renamed Hold And Modify (HAM) to get more colors on screen. He convinced Jay to include this feature.
Daphne had a control bit in the BPLCON0 register, bit 8. This enabled RGB or NTSC mode, affecting how the 12 bits of color would be interpreted. In RGB mode, color bits 0-3 are for Red, 4-7 for Green and 8-11 for Blue. In NTSC mode, bits 0-3 are for Y (Luminance), 4-7 for I (In-phase) and 8-11 for Q (Quadrature). I and Q are 90 degrees out of phase from each other and modulated together to generate a color (chroma).
When designing the first silicon, Ron suggested taking Hold And Modify off chip. However the feature was kept in at the request of Jay Miner, Dave Dean and Dale Luck, who predicted someone would find a use for it. Jay would later instruct one of the CAD techs at MOS Technology to remove HAM but was told this would leave a hole in the middle of the chip. The original HAM would be replaced with HAM6 for Daphne's successor, Denise.
NTSC encoding was reimplemented off chip by Dave Needle. The composite and TV video on the black box are generated using two MC1496 balanced modulator chips and several resistors. A Motorola MC1377 was used for the production Amiga. Bit 8 in BPLCON0 was later reassigned to enable audio for the genlock and renamed GAUD.
References
- Joe Decuir & Ron Nicholson at the Amiga 30th in California - Uploaded 10/7/2015
- Amiga Speech by Ron Nicholson (Amiga Ireland 2023) - Uploaded 1/17/2023
- Nicholson, Ron. Jay Miner Tribute - Usenet - 7/8/1994
- Peck, Rob. Amiga Hardware Manual (preliminary) - 1984
